MX1000!!!!
Oh and by the way, I game with it as well. I do have the set down lag but it doesn't bother me since my mousepad is massive and I never or rarely have to lift the mouse. If you're a hardcore gamer and don't have much desk space, then I don't know how suitable this mouse is for you.
However, this mouse is hands down the MOST comfortable mouse you'll ever have. Holding it just seems so natural. As long as you don't lift the mouse, gaming on this is great although I haven't compared it to an MX510. If you're not a hardcore gamer however, I highly recommend it especially when you compare to the MX700.
Just my $0.02