I didn't see a single review about the gigabyte model "overheating"
If a unit overheats, its faulty and should be rmad. these cards are fine with cooling.
as for 2.0 vs 3.0 , does not matter currently.
the x16 etc. also doesnt really matter to you atm

The 390 is a better card than the 970.
Ill give you a copy and paste of mine
Quote
the 390 has 8gb of vram, the 970 has 4gb of vram, but theres a technical detail that .5gb of that vram is about 8x slower than the rest, which can cause issues if you are using more than 3.5 gb of vram. I have not tested myself, but many complain about this.
The 390 runs hotter than the 970 and consumes more electricity. Though for other people ive done the math, and the cost difference in electricity is very small, unless you pay closer to 30 cents per kwh.
In terms of performance, the 390 usually ties or beats the 970, especially at higher resolutions because it has more vram, which is what higher resolution gaming consumes more of.
my personal opinion is that if the 390 is same price or cheaper than a 970, always get 390 since it offers better performance in general and has 8gb of vram, which may protect you as developers are using more and more vram due to the consoles having nearly 8x more ram in general than they have in the past generation.
This post was edited by Rapture on Nov 14 2015 09:38pm