A Simple Question Really...

[fishy_fiz]

I used amithlon/os3.9 as my main system for years. Winuae is nice in it's own way, and has the advantage of also having custom chipset emulation (amithlon is rtg/ahi only), but for my tastes it's never felt quite right and amithlon has always been the better experience. It has less hardware support, but with a little shopping around its not too difficult to get a fully supported system, even with modern gear. No host OS is required (well technically Amithlon is the host OS (a customised linux kernel) , but its minimal to a point of never being seen). It's both faster than Winuae and unlike Winuae everything is done from within Amiga OS (drivers, uses amiga os tcp/ip stack,etc.). It's also possible to use native x86 amiga os3.x software from within 68k AmigaOS (although not a lot has been compiled for this architecture) for even more speed. Even when my a1200+bppc+grex1200/voodoo3/256 meg fast system was functional I found Amithlon to be the best OS3.x experience. As for what advantages either bring over classic hardware it mostly comes down to just performance, which in turn opens up new doors to OS3.x.... high res video files run flawlessly, duke3d, quake, quake2, freespace, napalm, and many other pieces of software that even the most expanded classics might struggle with run nicely, various emulators (mame, megadrive, super nintendo,playstation,etc.) all run great, sdl software is suddenly more than usable, compiling times drastically improve, lots of room for OS enhancements (afa os,etc.) without hurting performance, 3d rendering software is drastically faster and so on.... in short imagine a classic amiga with an '040 running at speeds 20x (and then some(sysinfo tells me I have roughly a 3.5ghz '040, but to be fair synthetic benchmarks and emulation dont always represent the true tale)) than that of the fastest '060. To suppliment the lack of custom chipset emulation there's also a 68k version of euae (I simply set up a def type to launch adf images with euae), although if you have a classic amiga already this may not be so important (although I also at one point ran my classic through a tv tuner card inside amithlon/os3.9)..... on an even modest pc you get 680x0 speeds in excess of what any available OS4.x hardware can provide for native ppc software. This is mostly true of Winuae as well, but if your interest in a pc is soley for what it brings to the amiga table Amithlon is the way to go in my opinion (assuming you can find it of course, as its no longer sold).
Now having said this it took a while, but AROS has gotten to the point where it's a serious alternate option. It doesnt run amiga software out of the box, but janus uae can create a fairly seemless intergration with things like launching software as normal from Wanderer (AROSes Workbench), aros menus for 68k software, mixing aros and amiga os software as though all native (cycling through screens with the screen gadget, etc.), full screen or windowed apps and so on..... a different method to either os4 or mos, but quite effective nonetheless and the advantage of full emulation and not just system friendly stuff. As nice as it is to have this however the real benefits of something like AROS (or os4.x/mos) is it's more modern software. Although there's probably no software that either have that couldnt be done for os3.x the simple fact is that it seldom is done and often if it is there's not nearly as much time/effort put into OS3.x versions of more modern software.... things like movie players, web browsers, sdl software (Of which there's a lot(although only a small percentage is decent in my op.)), 3d/gl games are all better experiences on the "NG amiga" systems.
Personally I still very much enjoy a lot of classic software and for all the advantages the NG systems offer I cant do without an os3.x system. Having said that though the same is true of the reverse.

[fishy_fiz]

^^
There had to be one didnt there.... very useful contribution to the originals posters questions......

[fishy_fiz]

For 2000 pounds you could buy an absolute monster of a machine. As for what to buy, I guess it comes down to how much you want to spend. With a budget of 2k pounds an intel i7 of some description is the best bet, being that its the most powerful consumer cpu available. These come in 2 different sockets, 1156, which is the more mainstream variant, and doesnt differ greatly from the socket 1366 version, minus the fact it uses only a dual channel memory controller as opposed to the latters triple channel controller. Both use ddr3 ram from 1066mhz through 2200mhz(or higher if you want to spend the money) depending on a users wants. Obviously the faster the ram the better the performance, but dont disregard things like latency either,.... typically better timings equate to better performance than the higher speed (in mhz) variant with less tight timing. A step down the ladder would be something like an Intel i5-760, which is still quite a monster, although somewhat more affordable and is also a socket 1156 cpu. Incidently both are quad core systems (apart from the high end versions of i7, (i7-980)which can be hex core). Additionally they also support hyperthreading, which effectively means the system sees the cpus as having 2x as many cores as they physically do (not entirely accurate, but for conversations sake its near enough). As for AMD cpus theyre still quite powerful (as are all available modern x86 cpus), but theyre delegated to the budget segment for a reason,.... they simply cant compete with Intel for pure performance (or thermally) in most situations. Beware the 6 core AMD cpus, as although they look attractive on paper (reasonable prices) theyre often no better than the 4 core variants, even when multithreading is involved (software that can take advantage of multiple threads/cores). Lower clockspeeds vs the top end 4core versions as well as identical caches (ergo less per core) and no additional hardware to deal with internal cpu communications see to this. Another thing to be aware of with AMD cpus is that they wont work with faster ram and are restricted to ddr3-1600 (can go higher with overclocking and luck, but dont count on it). As for the very budget segment neither Intel nor AMD own this market in a clear manner. AMD is traditionally cheaper, but in terms of performance you get what you pay for, although the scales probably tip slightly in AMDs favor, especially for heavily threaded software (AMD's athlon x4 and phenom2 x4 cpus are quite cheap), although per thread Intel has the advantage. As for video cards, this isnt as clear as it was a few months back either. Had you asked then ATI/AMD wouldve been recommended without question for pretty much all pricepoints, but despite a few teething problems Nvidias Ferni range of cards are also a good buy. The new 104 based gpus (460) look especially attractive for thier price point. Really though apart from the budget segment (under 130$ where AMD are probably your best bet as they offer both superior performance and feature sets) you again pretty much get what you pay for with the exception of the afforementioined gf104 based gpus (460(which is both cheaper than a 5830 and performs more like a 5850, which is proportionally considerably more expensive)).
This is all assuming you go the non brand name PC route. A brand name usually adds a little to the price, especially when that name is Apple. While I have nothing against Apple products I'd never buy them myself as they simply dont offer the value (in terms of raw performance) I want. Others see value in different terms, and for them Apple products are worth the money (software bundles/osx/etc.).... each to thier own though.
I hope this is info. is of use to you and feel free to ask if you have any more questions.
p.s. Unless you want the absolute best available it'll be heard to spend 2k pounds. An Intel i7-860, 8 gig ddr3-1600, radeon 5870 (or nvidia 480), 2 terrabytes hdd space, bluray reader/writer, nice shiny case, nice sound card and 7.1 surround system and so on could be bought for well inside 1000 pounds...... you can of course go dual gpu, i7-980, etc., but Im assuming something that that would be overkill for you.... the above (or something similar) is a very nice "standard" high-end type rig.

[fishy_fiz]

The only problem with waiting is that there's always something new around the corner, so by the time what you're waiting for is released there's something else new around the corner again. Personally I'd go Intel at the moment, moreso becuase there's scope for improvement,... the am2/am2+/am3 systems have gone about as far as theyre going to with no scope for upgrading without the main core of the system being replaced. Little disappointed to say that really, I used AMD exclusively for quite some time and do like the barrack for the underdog, but when money is involved Im not one to let brand loyalty get in the way. Having said that though an x4 955 or 965 is still an ok machine, especially for thier price.