There are more to machines like the PS1 than just their CPU core, what about the video core and sound core? all of these parts require a certain amount of cpu time.
Besides, my machine runs the emulator at a 4 times faster framerate than the original machine, so in theory 800mhz *should* be enough, asuming you have excellent video hardware to go along with it.
N64 emu requires more than 10 times its cpu power as well, because of cpu core, graphics and sound as well. all depends, it doesn't have to be "optimized", as long as it works. considering how much it costs to upgrade to a better system I can't understand why you'd still use an 800mhz processor.
PSP definitely can't run ps1 emu at full speed, unless its doing something like the n64 emulator Corn used to do, which is static recompilation; it's basicly a hacky way to make a game run and only one game would work. I'm commenting on you saying ps1 emulators on the PC are unimpressive, like hell they aren't.
behold:
