So which one works better for FPS games?
G700 is tried and true. It consistently gets great reviews from users. It is my favorite mouse design by far - workstation, game rig, laptop, etc... Button placement is great - I love the look and texture/feel of the old black models. I have not used the new model G700.
The 602 is new, so you probably won't get as many reviews or comparisons with it.
It looks quite different in form factor, and I've never been a big fan of the thumb button clust (ala Razer Naga).
Head down to the store and play with both, see what fits your hand better.