when not gaming and in 2d mode either graphics will run at slower than advertised clocks to save energy, once you open the game up clocks for memory and core will increase to the advertised settings so yes they will underclock themselves when not in gaming
Why are you going for a GTX 680 or HD 7970? Do you have multiple monitors? If not, why don't you step back to a GTX 660 or HD 7850 2GB? Expecially after underclocking, you'd definitely lose performance there. You'll save power and still be able to perform well as they both have 2GB of VRAM so you'll be able to crank the AA/AF up.
Yeah... you don't technically need a 7970/680 for single screen gaming. Of course, it's your choice and a 7970/680 will absolutely max everything out at that resolution and keep you from needing an upgrade for a while, though
Yeah, exactly what I desire, and the "one gaming monitor" is a variable too
According to hexus.net idle power consumption is 49 watts. Is it impossible to go lower?