don't by the 9650, i think they are out of the game now, you can buy a phenom ii 965 for cheaper than the 9650 and it is about the same or slightly better. Get the i7 920, it only costs a bit more than the phenom ii 965, in some games i believe the core 2 9650 actually does better than the i7 920, just like the phenom ii 965 does better in some games than the i7 920. Buy the cheapest, except if the i7 costs not a lot more buy it for sure.
however it would be a good idea to try out a quad core, maybe if that person has the money to spend, with a quad core you can try out mass multitasking as well which you wouldn't have been able to do with a dual core. But if you're just wanting more performance for games and games alone then stick with the e8400.