In it's current state the engine was designed on/for nVidia chipsets, virtually no AMD optimizations were included, easily one of the biggest failings it suffered and continues to until 2.0
So the answer here is, wait until 2.0 engine lands so we can see what they've done to improve it's ability to properly utilize AMD chipsets. nVidia support wasn't/isn't even great but it's light years ahead of the current AMD support.