I would think that the first $3K or so, for a serious "hardcore professional gamer", would probably be better spent on a state-of-the-art gaming rig rather than the internet connection (use DSL instead?), but what do I know.
I do happen to know someone that was in the top-ten internet rankings for UT, and he could still play at my place over DSL, using a relatively slow and crappy system, and still own. Using a better system, I was lucky to get into the top three spots on those servers, even with just as good a ping.

(I do much better, playing on LAN games - I'm not sure why.)
Just as important as the connection speed (I assume dedicated bandwidth with a T1), would be how it is connected to the internet, peering points, etc., and where the other players are located, network-wise, in relation to him. Unless he's hosting, then if there is a slow/overloaded router between him and whomever is hosting, and someone else is "closer", network-wise, then a T1 probably wouldn't help that much.
What are the ping times like on a ("residential") T1 anyways? I'm rather curious.