I am not sure I agree anyone cares about efficiency that much.
What it is all about is what you are spending your watt's on.
No matter what until retail hits the street's we will have nothing definitive.
The speculation is the performance for the watt's spent is not going to be there.
This card will be an epic fail if it can only deliver 10% over a GT980.
The higher that percent actually ends up will be tell tail to if this card will succeed or not.
Just like with the GTX480, was it worth the heat and power consumption for the performance or wasn't it ?
The alternative the more efficient, cooler running 6970 at about a 15% deficit in performance.
They sold a lot of 6970's despite the gap in performance.
Point being this is not a new argument, simply the same one with the rolls reversed.
I am sure many will jump on the 390x if it is 10% faster or better.
Many will opt to use the GTX980 though
Back then if you remember NVidia was scrambling for a solution and the GTX580 was released shortly after the GTX480 in an effort to regain market share.
The GTX 480 was a great performing card. slightly better than a 570 and overclocked better than a 580GTX because the 580's and 570's had terrible power delivery issues(they would often just die).
Yes it was hotter , yes it used more power but it had just as good or better potential imho than a 580gtx.
That said the 6950 sold tons and the 6970 sold well .. Why?
Well for one most 6950's could unlock to a 6970 I unlocked 3 in my time with them.
They were also under 200$ i paid 150$ for the last 2 i bought and that was prior to the 7xxx series cards so they weren't last gen yet.
That and all the 6950's i unlocked to 70's overclocked a good +25%.
The GTX570 at that time was nearly 2.5-3x that much and the GTX 580 was 500$+ only 8 months after the GTX 480 released.
I owned both @ the time i still have the GTX480 in a guest pc. they all worked fine with similar options but the AMD cards were much much cheaper.
If a friend had not wanted to buy my 6950(70 converted) id have prob been using that in my guest pc now.
Either way --- Yes Price Vs Performance has much to do with purchasing.
I could care little about actual wattage use tbh .. I never will either, so long as it performs well and is manageable heat wise. I never leave my gaming rig on past the time i use it anyhow so power use is totally not a big deal to me.
I doubt it is to most other people either.
If AMD made a 500 Watt GPU that did 6x the performance of a 980GTX and ran off a All in one Liquid cooling unit that took 2x120mm Rad people would buy that thing as long as it was afordable .. heck even if it was double the price of a 980 they would still buy it for the performance.
Problem is AIR coolers have hit their limits which means 1 thing.. either increase efficiency or they cant continue to use air coolers.