Im using latest driver 16.8.2 with Dolphin (SuperSmashBros Meele,) and ePSXe (Silent hill, Spyro series) and everything is fine. Try latest development version of Dolphin. It always works better for me than stable.
Just version 5.0 Cemu is still very early in its release and alot of games still dont work, out of the games I tested I had more that wouldn't work than did work. Mario worked fine though.
CEMU is not ready yet, the creator even says that on the site. Use DX12 with Dolphin, the difference is night and day. Also the emulator creates shader cache files the first time you run games with a new API selected, so you will have stutter as it creates the shader cache. This is expected behavior and completely normal. Just stick with DX12 with Dolphin for a while (until you have shader files for all the games you actually play), and you'll see what I mean. Performance is amazing.