I didn't try out older os, first of all because i don't have one. If you disable visual effects in winxp @ ps3 it will run a little faster. I have a PIII 866MHz overclocked @ ~950Mhz 192mb SDram and compared to the emulated WinXp they run fast as hell.
I don't think the way of emulation is fast. I think if ps3 had more RAM it will increase quality. Ps3 uses Elpida ram. If someone brave enough install more ram-chips (if it has extra slots) or remove and out higher capacity RDRAM, it would be great! Xbox has a similar mod.
Eternal, i didn't tried other OS emulation, because i don't have anyone of them. I don't think emulation is the best way. I have a PIII with 192mb SDram and it runs compared to ps3 fast as hell. It can run Photoshop 7, Nod32, Firefox in the same time w/o stuck...
If ps3 had more Ram i think it would had been an improvement. PS3 uses elpida ram chips. If someone brave enough tries to change the chips with larger RDram chips it would be amazing! Xbox has a similar mod.