I think your cpu is already bottlenecking your hd6670...
What model and serie is your cpu?
I'd upgrade the cpu, not the gpu...
On what resolution do you play?
ok so what is the best gpu i can get for around $130
and yes i am planning to upgrade my cpu to a phenom x4 but for right now i am stuck with my athlon ii x2 i think its the newer generation one.
Get a cx500, a phenom II x4 965. (Or if you want to oc, you can always take a lower one) and a hd6850/hd7770. If you got the money, a hd7850 or gtx660 (non ti) are great deals.