If your running stable in Windows and 3D apps then I'd say don't worry about memtest. Prime95 is a lot more stressful than memtest and many people have proven that even if your ram passes memtest that doesn't mean that it will run stable in 3D modes such as games and benches.
Edit: I have the same issue with everest, I'd recommend running it multiple times per setting change.
Edit: I have the same issue with everest, I'd recommend running it multiple times per setting change.