The Ti over the MX is a very good investment. I use the Gainward GF2 Pro and my games all perform pretty well, for the price I paid for the video card, and what I have is slower than the Ti, actually. Only game I've ever seen real nasty slowdown on is Medal of Honor: AA, in the German forest multiplayer level..
For a CS, Q3, UT computer, the card fills the role perfectly.