Ok I just tested Momodara IV and Quicksync won, no contest.
Color accuracy and saturation was way better than NVENC. And even with NVENC set to 4 b-frames (optimal for a game with relatively low screen movement), it still didn’t resolve every pixel fully. Certain edges and corners (such as dialogue boxes) were muddy.
I really cranked up X.264 with a lot of extra options. It matched Quicksync’s color saturation and generally looked the same. Until…I started fighting enemies. Once I started attacking and darting around—X.264 had trouble keeping up and resolving all pixels, during such motion. Even though I had lots of extra motion options turned on for X.264
Quicksync had perfect color saturation, sharply resolved every pixel, and was able to keep up with motion, with zero artifacts.
I’m gonna go on a limb here and say Quicksync, if you have it (sorry AMD) is the best choice for 2-D pixel art games or old games like NES and SNES. I still need to test a 2-D fighter. But have a feelling Quicksync will shine there, as well.
*remember, I have a Kaby Lake i5 7600K processor. Older versions of Quicksync may not look as good.
*I just realized I have a laptop with an Ivy Bridge i5. That’s 4 generations older than Kaby Lake. I will compare the Quicksync on that, very soon!