Is there really this big a difference between AMD and NVIDIA? As i am thinking of builing a system with a evga 670 i was wondering how much better a similarly priced AMD card would be in mining?
The bitcoin wiki
shows a hashrate of 406MH/s for the GV-R787OC-2GD  (a $250 card) while the EVGA GTX670FTW 2GB gets only 112 MH/s (a $400 card).

This seems really off to me. Is there really this big a difference?

As on many websites it says AMD is so much better for mining while because NVIDIA has Cuda everyone says its best for editing why doesn't cuda drive up Mhash/s?
Is there really this big a difference?


Yes.


  As on many websites it says AMD is so much better for mining while because NVIDIA has Cuda everyone says its best for editing why doesn't cuda drive up Mhash/s?


CUDA's a software framework for making GPU-based software eaiser to write. More stuff supports NVIDIA cards. Bitcoin GPU miners support both, so CUDA doesn't matter.