for the 2d games seens that there's nothing you can do, they simple or work very fast, or work in a middle speed, if you have an OK PC ^^
for the 3d games, they depend heavily on your graphic card it seens, in these games a good graphic card can give you a very good boost of speed
but take it with a grain of salt, the only games that i have tested was, Bleach Heat the Soul 5(works ok),7(its slow, but the framerate say its ok, but the gameplay is still slow),Dissidia Final Fantasy(works ok), Kingdom Hearts Birth by Sleep(works ok),Valkyria Crocniles 2(totally playable with sounds and stuff)
if you're using windows 7 you can use the magnifier it makes the emulator a little faster it seens i'm not sure
for the 3d games, they depend heavily on your graphic card it seens, in these games a good graphic card can give you a very good boost of speed
but take it with a grain of salt, the only games that i have tested was, Bleach Heat the Soul 5(works ok),7(its slow, but the framerate say its ok, but the gameplay is still slow),Dissidia Final Fantasy(works ok), Kingdom Hearts Birth by Sleep(works ok),Valkyria Crocniles 2(totally playable with sounds and stuff)
if you're using windows 7 you can use the magnifier it makes the emulator a little faster it seens i'm not sure