Hah. I forgot the conclusion.
So if this all works we basically end up with a 300 MHz CPU connected to DDR memory running at close to the same speed as the CPU (latency is high, but bursts are good) and USB and ethernet ports close enough to the CPU to run at full speed. The Mac motherboard becomes a peripheral interface, which happens to provide the ROM code as well.
Even with the instructions which will throw execptions I bet this would run at least four times faster than a IIfx and maybe better.
Video performance would still be abysmal though.
So if this all works we basically end up with a 300 MHz CPU connected to DDR memory running at close to the same speed as the CPU (latency is high, but bursts are good) and USB and ethernet ports close enough to the CPU to run at full speed. The Mac motherboard becomes a peripheral interface, which happens to provide the ROM code as well.
Even with the instructions which will throw execptions I bet this would run at least four times faster than a IIfx and maybe better.
Video performance would still be abysmal though.