I must say that I didn't have any problem benchmarking amd cards: if the room was hot, I'd put the fans at high speed, run the miner and wait a couple minute to stabilize, and that's it. I could make 100 changes to a kernel in a day and check them all, accurately.

On nvidia I have throttling problems I can't easily fix (the cards reduce clock speed in a number of situations I just can't predict), overclocking/downclocking is more difficult as the cards tend to change clocks by themselves, and the hashrates fluctuates wildly, and even changes between ccminer runs.
The rig is headless so I only have nvidia-smi to work with, and it can't set the fan speed.
So when I make a little kernel speedup, I spend more time benchmarking it (to be sure it's indeed an improvement), than making the improvement itself :-/
Maybe there are some nvidia-smi settings to make it more stable?
Or maybe on windows it's different...
Finally I may need a workstation with a nvidia as main card, and work on it.