The MX500 and 700 are EXACTLY the same in build. The only differences are:
A) 700 is wireless
B) 700 is heavier (battery weight)
C) 500 doesent loose power suddenly
D) 500 is cheaper.
The both use the 800 dpi optical laser on them. There are no differences. They both have the same buttons, same layout, same design, and same shape.
For gaming, I would reccoment the 500. Its cheaper, lighter, tracks fast, and is gread for normal desktop use (the ergonomics feel nice in your hand)
However, just to show a comparision, Microsoft mouses tend to be a little less high quality (but its not noticible when you use it), but cheaper mices. Most of the MS mice dont have 5 programmable buttons like the MX5-700s do, and some people argue that the ergonomic MS mice dont feel nice in your hand. But their still good mouses for cheaper.
Beemer: The optical mouse shouldnt be jittery for selecting pixles. Ball mouses track FASTER, but not more PERCISE. Opticals are more percise, and with the speed of the MX series, that shouldnt be happening :\.
If you're really into gaming, you might want one of the hybird ball-optical mouses that track at 1800dpi (yea yea, thats insane). But if you're into heavy gaming, its really worth it. Check them out here:
http://www.bestbuy.com/site/olspage....059&cmp=%20%20
Great mouse if you have that type of desire and/or money.