If you move your mouse very quickly when gaming bear in mind that any Avago 9500 mice (G500, CM Sentinel, that new-fangled Spanish Ozone SMOG thingummy etc.) have very low max perfect control speeds (MPCS) and malfunction speeds, i.e. it doesn't take much to cause the mouse to wobble perpendicular to your actual movement or stop tracking and even less to cause negative or positve acceleration.
I'd say go MX518 if you want a sure fire piece of kit, if you want to be different ocUK seem to be stocking the Diamondback 3G again, or even more different there's the Sharkoon Fireglider, Razer Boomslang CE2007 or the Abyssus (which razer just released a mirror finish version of) although I don't personally care for it too much without DPI adjustment on the fly (I didn't think it would be a big deal 'til I started using a high DPI mouse) or thumb buttons.