In regards to emulation speed, the truth lay somewhere in between what people have suggested so far.
On a high-end, new pc interger performance of emulated system probably eclipses any available "amiga" hadware. FPU performance however is more in line with old phase5 ppc cards.
UAEGFX now also works with os4/ppc, and apparently also supports compositioning. Voodoo3 support is also coming (old h/w, yes, but mentioned for sake of thoroughness).
Given time winuae will surpass any real hardware in pretty much any measurement, exactly as it did when amiga was 68k. Its already a viable option.
And contrary to how it may sound Im not particularly endorsing it to anyone. Nor am I denouncing it. Im simply stating how things are.