Are you sure w10 did not change your vid drivers and you not know it- w10 does do such things.. W10 might have messed up your vid drivers- if not already I would check and or delete the vid drivers and get newest from nv and do a clean install- also might not think so but if adobe flash needs updating it can make your system run crazy- would also clean browser cache and turn off all extra stuff when trying to play- I turn off security all of it when playing- not like am multi tasking and surfing the net while in game.. Could it be heat- when was last time you cleaned or blow it out with air etc.. and yes should set your monitor to native res and hrz etc- set game same as monitor native too.. Unless I am wrong- those are dx9 games and that 660 should run dx9 fine with all maxed settings..
74 hrz is an of number- unless the game caps- the vid card will try to run fps same as refresh which would be 74fps- set to 60 and use vsync- or if not tearing turn off vsync- I know when recording vsync could give me probs in some games and is not needed if not tearing- so what if runs more than 60 or 74 etc fps.. I am on a gsync 1440 monitor now but did notice such before on my 1080 monitor.. The games could have updated too and I have read that both those games are buggy- could be the games and not your system at all..