if gaming i would say 3800+ non X2 would be better becuase games arent 2 threads, although office work, multitasking, etc the X2 would benefit.
the 3800+ is 2.4 GHZ
and the 3800+X2 is 2GHz, the extra 400 MHz will help alot in gaming and get good performance ram, like Crucial Ballistix