Logitech are crap, they make crap mice, i'm not a razor fanboy or anything but i'd rather game with a microsoft mouse than a logitech, infact I did for about 2 years.
Logitech mice are heavy, ugly, and uncomfortable in the hand and the buttons really suck.
I have the LE diamondback now and i couldn't be happier with it, very low contact friction, supurb buttons. The mouse is very sensitive which takes a little getting used to but trus be once you do you wont want to go back.
as for features etc WTF? this is gaming we're taking about, you need a wheel and two buttons.