Knowing what games you're trying to play would help. They might be games that aren't emulated as fast as others.
If that isn't the problem, though... you might want to try overclocking the emulated CPU by pressing the "+" and "-" buttons over on your number pad. You can tell what you've got the CPU set at by the little green numbers below your frame rate. Normally it reads "CPU 100", and after you adjust it higher by, say, 20 points, it'll say "CPU 120", etc...
It can help to (safely) get a few extra frames out of your game.