Wife had similar problems with win10 and NVidia card. Found a temporary solution by turning off V-Sync in the NVidia control panel, but that caused the in game frame limiter to not function either, which meant the card was going full throttle all the time. It also only worked for a few days then went back to random fps drop, appears to be related to one of the bajillion Service host processes eating up CPU time. We ended up reinstalling win7 and haven't had an issue since. Have heard about this issue effecting multiple mmos and some offline games with NVidia cards and Win10.