What gpu would work well with a Alienware m17x R3



No need to hate on Alienware i bought it from a friend for $700.
Specs:
Intel Core i7-2670QM CPU @ 2.20GHz
4.00 GB RAM
NVIDIA GeForce GTX 560M
Intel HD Graphics 3000
Windows 8 64 bit
 
I have recently upgraded my Mx17 r3 to the 6990m an it works great, currently im looking ot upgrade to the 7970m but I'm tempted to get the 8970m but that might require some technical know how. Alienware is still going hard, love it to bits, hope this helps