In terms of the speed difference required to emulate a different CPU architecture at full speed, I've heard numbers between 6x and 12x, which probably makes sense if the PSP emu needs a 2GHz x86 CPU to run full speed. Also keep in mind that clock-for-clock I think that (even one core of) a Core 2 Duo is faster than our little Cortex A8. Starting a PSP emu now and hoping that it will run closer to playable speed (maybe without ssound?) on a dual-core Cortex-A9 OMAP4 sometime in 2011 or 2012, might be a lot more reasonable. Hopefully they'll (ARM? TI?) get us more internal bandwidth by then...

@davedickson: I definitely think you shoulc do your proposed qemu experiment. Even if it doesn't turn out to be "playable" I think it'll be a lot of fun and you'll learn a lot on the way. If you want advice on where to get started, stop by #maemo with an open mind and some free time.

-John