Recommend a gpu for video editing

My friend is building a new machine with video editing going to be it's main use. 

He has all of the main components so far with the exception of a graphics card.

The main piece of software he uses is Sony Pro Vegas 12. He can change to 13 if there would be performance increases.

His budget is up to £400 roughly.  

Any suggestions which would be the best to go for ? I was thinking a R9 290X since the price has dropped to around £220 - £230 or would an nvidia 780 ti be a better option at around £350 ? Or are there better cards to pick ?  

Vegas uses OpenCL to do GPU Acceleration, so for the best performance AMD is the best choice at this time for OpenCL. The 290X also benefits from having more vRam and a wider memory bus. 

 

Sony vegas indeed loves open cl

i would grab a R9-290. probably a bit cheaper then the 290x.

Sapphire 290 TriX OC  or Sapphire 290 Vapor X.