I have used MX518 for more than 4 years and that is a single gadget which can never be complained about....For MX518, I switched to DeathAdder, then to Intelli....Both of them were nice, But once you have used MX518, It becomes quite tough for any mouse to be at the par..I purchased X5 and this one proved to be the one which was really awesome. I can guarantee that this is probably the best mouse in the market for Professional Gamers. Its Perfect Grip definitely gives an edge to it. Unbiased Opinion : If you can get MX518, go for it (I think, that model have already been discontinued), else go on for SideWinder X5....However, at the end of everything, your gaming skills matter much more than the mouse and its specifications.