What you may be seeing is the GPU hitting the end of the road. I'd change my GPU first.
Again the CPUs have the SAME 130W TDP so that removed a concern I'd have. Be sure your BIOS is Dell's latest BEFORE the change.
I have an Area 51 by Alienware, it came with an intel i7 core 930 @ 2.80 ghz and I want to upgrade to a 960 @3.20 ghz. They both use the same socket and chipset. I can not find any useful info on my mother board.