i have a trek 4500 and am ready to start making upgrades. everything is currently stock and i think the first and best move would be a new rear derialler. I was looking at the xt and xtr, i like those better than the grip shifts of sram. any other recommendations for upgrading the bike? i was a smooth ride. also i was looking at changing from my matrix 750 rims and was also going to grab some continental travelcontancts for commute days. just trying to get some feedback on several different things. (oh and it is a 24" frame,i'm 6'8" 250)and was wondering if the upgrade to disc brakes was worth the money