Thanks, I will try that. So if I go with say a 6950 my CPU would be a bottleneck? Would I see any improvement?
No it wont and yes you will see a decent improvement. Percentages don't really tell a true story but for this they will have to do,
the 6950 is about 40-45% better/faster than a 4870, if you get a 2GB card then you have the option of trying to flash the bios to a 6970 as well.
A better CPU will give you better performance, that would be a little dependant on the game as well but your CPU certainly wont restrict the performance that much.
Take a look here http://www.tomshardware.com/reviews/core-i3-gaming,2588.html