Your i5 running what software?
Several. It's a Linux system. I've tried eUAE, with rather mixed results giving me a system that boots incredibly slow even when emulating a 68040 at full speed (no speed brake active, really), so slow that I can see the workbench drawing the background image tile by tile. Then after a minute, it seems to recover and then works for *most* things at acceptable speed. Something's broken.
I've tried fsUAE, which I cannot even use due to its interface. I've found no menu or no button how to setup a harddisk, or to define the kickstart, so I gave up before I could measure anything. It's ok to insert a game disk - that's something I see in the user interface. Unfortunately, I'm not really into games.
I've put *a lot* of work into vamos in the last year, which runs acceptable, on top of the musashi 68K emulator. It's not a particularly fair comparison because it is not a high-performance emulator. The speed is better than my 68060, but not stunning. Without having made detailed measurements, I would say that this is probably a factor of around two at most. Workable, but nothing to call home about. As said, it's a simple emulator, no JIT. Gets the job done I wanted to do, but probably nothing to build a hardware around it.
Putting an intel chip onto an amiga motherboard might seem like blasphemy, but it would have even less overhead than amithlon. The only annoyance is big vs little endian.
It's no more or no less "blasphemy" than putting a PPC on it. In the end, if running "foreign" code on it, an intel is considerably more useful than a PPC. At least, there is a software library for it. Concerning emulation, I wouldn't hold my breath - but as long as you have the chipset available instead of depending on emulation, it might be more workable than eUAE.
The best implementation would essentially be a modern bridge board, so you could run pc software on it at the same time as running amiga software. Or have it run a 68k emulator and access the amiga motherboard resources. Bonus points if you can make the keyboard and mouse appear as standard pc peripherals, not sure what you'd do about the floppy drive. But it's a dream, power would be tricky but doable, cooling would probably be harder.
Well, that sounds much more like a plan than the PPC experiments here in Amiga land, if you ask me. It would also give you a computer that could do something productive (ehem) if you don't want to run it on an Amiga.
The problem with emulation is really that - depending on what you emulate - the performance might be "very reasonable" to "dog slow", and that on exactly the same machine. See my experience with eUAE. Depending on what I do, it is quite acceptable (excluding anoying user interface glitches, another discussion) to "unbearably slow", as soon as you do something with the chipset.
Yet again, it is a matter of your problem definition: For me, the primary purpose is 68K code execution, and *for that* the vampire is just an excellent solution (or might become one, depending on your needs). A x64 might also be a *workable* solution, with an added bonus on top that you could also run something "useful" and "productive" (i.e. "non-Amiga", excuse the irony) on it.
What I need a PPC for I still haven't really found out. Nice machine, sure. But that's all about it. Yes, I do have an old G3 Power Mac at home, 233Mhz, ATI graphics. Works - that's the best to say about it.