I am hoping to do the 970M upgrade too - the 680M just isn't quite enough for Oculus Rift. I guess because you had the 7970M you had no Optimus but AMD power switching instead. Good luck indeed, I'm especially interested in 680M in M17x R4.
This is good. I have had good temperature improvements (3-4 deg) simply letting the rear of the R4 sit an inch off the surface. This provides far more are in through the hole on the bottom. Nevertheless I still run at 81 degrees sometimes (680M). Getting old, this notebook now! It's been a good workhorse.