I think the relative prices you can purchase each for should matter. Also, if you overclock, you're right, I think that GTX 970 probably gives you a lot more headroom than the 390 would... something to consider. If you plan on doing only 1080p gaming, I don't think the 3.5 vs. 8GB of VRAM would matter. For 1440p+ gaming, 390's 8 GB of VRAM would probably suit you better.
I'll leave more detailed comparisons to the folks here who know every piece of data to cite 🙂.
I'm worry my Corsair HX750 won't support power hungry R9 390.
Unless you're heavy ocing the card you're ok.You can run two with an HX750. Power consumption figures are way way way overblown here.
The point is that you are getting a 4gb card in which the full 4gb doesn't work at full speed and only 1 portion can be accessed at a time.Is there any practical problem to the GTX970 memory scheme though? I'm buying a 390 (in anticipation of Fallout 4 texture mods), but articles I've read on the 970 written after the 4GB debacle was discovered say that it was really only problematic in situations where the card lacked the power to deliver playable frame rates anyway.
Why not just get the FTW version at $300? It's not like you really care if it's new or not? It's the best chip you'll get and it's still lower than the 970 and 390 (well not the XFX 390 though).
I'd probably get the XFX 390 for $290. This generation, you want to get the best bang for your buck while accomplishing your goal.