All this ps2 talk is quite interesting. I'm looking to sell my ps2 (with 21 games, multitap, memory card and some contollers).
I tried to run my fahrenheit game on pc emulated, and it was slow framerates, despite having a quad core cpu, and a half decent graphics card!
My advice: Keep the PS2 in case you want to emulate later or ever feel the itch to play again....unless you have a (rare) PS2 compatible PS3 anyways. Some of the games for PS2 are damn fun to play and not having a PS2 can suck bigtime if you ever want to play it again(or if you want to emulate "legally" by having a ps2 when you emulate games you own.)
As for the slow speeds, it depends on the settings you pick for graphics output, as well as what plugins for graphics/etc you use. Setting the settings too high or using outdated ps2 emulator plugins can cause lag and bugs, afaik.
I just bought a PS2 for thirty bucks at Gamestop. Works great. Fun to play those games on the TV. Cheap! Cheap! I couldn't be bothered screwing around with emulating myself when I just play the real deal on a bigger screen. :-)