Most bang for 600 USD?

[psxphill]

Oh and for ARM emulation of 68k, it's a nice idea but will wreck cycle accurency and lock-step.

When you add any accelerator to an Amiga then cycle accuracy is no longer possible. The point is to make it run quicker than any 68k Amiga ever made. Most software won't care & if it does then it's most likely broken. It's not like the c64 where the processor is in complete synchronisation with the vic and sid.
 
Using one of intels new low power processors would be interesting too (like the atom). The choice should be made on whichever gets the most performance for the price (within reasonable price limits of course). AFAIK they are all little endian, so some performance would be lost in the conversion either way. Although ARM is 3ghz, that doesn't really mean anything. Instruction throughput is what you need to consider, it's entirely possible that a 1.5ghz processor can beat a 3ghz processor depending on their design (the p3 vs p4 came close).
 
I have had a similar idea for a while and would be prepared to put some time into the software side.

[psxphill]

A lot of software for the A500 did operate in a very hardware dependent manner. I guess it's the same for A1200. The common denominator is a simple and thus cheap machine and cheap machines that are good sell a lot (usually). That's why other models doesn't really apply.

There are some games and demos that got upset if the processor could run while the blitter was stealing bus cycles as they didn't bother to check for the blitter to finish. When the A3000 came out things started getting better as you couldn't rely on the user to turn off their accelerator.
 
However this can be solved without cycle accuracy, disabling caches and running from chip ram would slow it down enough for it to work. There are patches for alot of software too. Nobody wants to spend $600 on something that can only run at 7mhz, if thats what you want then buy an a500 or a minimig.

[psxphill]

USB* can get 480Mbit/s, although with 32 data lines and 24 address lines it might still be a bit of a bottleneck.

The problem is that the fastest speed is when you're transferring alot of data. You're going to have crippling latency doing individual reads and writes. If you use a USB serial adapter in dosbox then it can't even run full speed at 115,200 baud. You're not going to get 14mhz even if you hit 480 mbit/s, with the latency I'd be impressed if you get 1mhz. It's likely to be much lower.
 
We know that you can run a 68k emulator on an arm board, it's the hook up to the amiga that is the problem. Any time you spend on using USB is going to be wasted and the results disappointing and not an indication of what you can achieve.

[psxphill]

This is true but when doing development you do one bit at a time, you start simple and get it to work first, then you worry about the performance. I've never produced anything for the expansion port before, just being able to probe the ROM from my PC would be a start.

When worrying about the performance means throwing everything away then you're doing it wrong. Doing development one bit at a time is good, but you aren't doing any bits that are worth doing.
 
Starting with the expansion port interface is worse than running before you can walk, it's hoping that you can learn to walk by learning to drive.
 
Talking to xilinx about something like this:
 
http://www.xilinx.com/support/documentation/data_sheets/ds190-Zynq-7000-Overview.pdf
 
is going to get you further. You might even get some advice.

[psxphill]

But the 8088 IBM PC was not actually built until Commodore 64 era so no whatever that is it is not a PC

IBM didn't invent the term PC. The Altair 8800 from 1975 was where the term Personal Computer origininated.
 
It's quite a meaningless term nowadays, in the I'm a PC advert Microsoft implied it meant that it ran one of their operating systems. Yet on the same computer you could run Linux or MacOS.