If its on medium settings I wouldn't see why a 5670 wouldn't be good enough, however if you would like to future proof and see a very large performance upgrade I would say get a 5770 or 5750. Thats if you only like playing on medium settings. a 5770 should be plenty to max out AVP @ that resolution.
Okay. Is the XFX Radeon HD 5770 1GB DDR5 PCIE Graphics Card HD577AZNFC good? or should I go with a different one?