Heat? Really? A modern x86 with a heatsink won't physically fit in the cases these boards go in. To be viable these cards must run cooler than the alternatives - that's part of the point.
> I wouldn't be surprised if software emulation on a low-power, cheap ARM core could beat it; JIT on a powerful x86 is apparently 5-7x faster.
The current boards are kept cheap - they're nowhere near using the fastest available FPGAs, and the cores keep making massive performance leaps iteration to iteration and have been tested and works on FPGAs more than twice as fast as the ones on the current Vampire boards. The publicly released cards are now beating ASIC PPC cores clocked 7x as fast on some benchmarks. If JIT on a powerful x86 is only 5-7x faster now, odds are they'll be able to reach parity with the UAE JIT soon.
> It's also the exact opposite of open source, being a proprietary core tied to a single-source commercial boards.
Which is entirely irrelevant to the point I was making.
There are plenty of problems where, sure, you could get an x86 or a powerful GPU and do it faster, but you'll be paying for it with power usage.
E.g. take [1] - they're making a modern M68k compatible CPU in an FPGA. They're getting performance that's beating ASIC ColdFire CPUs (Motorola/Freescale's M68k descendant) and ASIC PPCs with several times the clock, and beating the fastest "real" M68k systems by a factor of 3x-10x.
You could beat that with a software emulator on a powerful enough x86, sure. Easily. Especially if investing enough time in dynamic translation and the like.
But this thing instead fits on a far less power hungry FPGA that gives off far less heat, and fits on a board that'll fit in one of the real small case Amiga's - try to do that with a x86 with heat sink..
[1] http://www.apollo-core.com/