Your absolutely wrong that cpu may be old but it's not weak.
It's enough for a 7850 with small bottlenecks, overclock it a bit and it will definitely do well but after a bit you will need a new cpu!
Please do not post false information. Here is a benchmark of the CPU compared to an intel g620. (bottom end for modern chips) http://www.anandtech.com/bench/Product/33?vs=406
As you can see it isn't even close to the performance of the lowest end modern chip that can be considered a 'gaming chip'.
The CPU will bottleneck a 7850 to the point of it being basically useless.