Ehh, the 4GB 290X is ~$400, the 970 at ~$440 and the 8GB 290X at ~$500. Honestly, one could go either way. Depends on he users needs and preferences.
Sure, but throw TDP in the mix? Heat output? Partially passive designs? Average OC headroom? Noise? Anyone into the hobby would consider all factors, not just paper specs, especially when there is $40 in it.
I dont really consider the 8GB card as a smart purchase since using that much VRAM on these cards is going to end up in non playable situations, unless you are running XFire, but again i dont recommend dual GPU setups. And if you are to run dual GPU setups, then AMD is in a good position. Pretty sure recent frame time analysis on dual GPU setups had AMD in front of NVIDIA.
970 OC results
http://www.bit-tech.net/hardware/graphics/2014/09/19/nvidia-geforce-gtx-970-review/12
290X OC results
http://www.bit-tech.net/hardware/graphics/2014/03/11/sapphire-radeon-r9-290x-tri-x-oc-review/9
They are pretty much neck and neck, but i wonder what the thermals are like and noise at those clocks on the 290X. I know my 970 peaks at about 68c in Far Cry 4 99% usage over a long period of time at 1545Mhz Core 8000Mhz Memory @ 1.23v. So i would assume the overclock bit-tech used would actually be around 65c. Thats assuming a 20c ambient temp.
In fact you can see the Sapphire Tri X 290X is already 10c hotter at stock speeds over a MSI Gamer 970 running Heaven bench.