Need help building a PC for the HTC Vive

[snyps]

fatslob-:O said:

snyps said:
I want to get a good enough VR with only spending $300-$400 on the build. What do you think is the most powerful card I could jam into my system to fall into the "VR works but not great" category?

If you have to compromise I would either get an R9 390 or a GTX 970 but preferrably the latter since you'll encounter front-end bottlenecks more often with AMD cards especially with your CPU ... 

Value wise is it better to go ahead and buy 390x/ 980ti since I'll get a new cpu down the road?