lol i think you need atleast 2 PSUs for this rig, even a 1200W will be hard stressed depending on its rail distrubutions.

I have to say at this time it's hard for any vendor to accept BTCs without risks.
The only benefit I can see is if you start early you get a bigger portion of the BTC market once it takes off.

if you do any gaming at all 6970 should do better performance, and offer better resale value,
but i doubt you can get any 5850 at $150 nowdays anyways.