Go back to the ORIGINAL CPU frequency, find a repeatable scenario or benchmark to establish a score, then test while raising the frequency.
There's something WRONG with the temperature reported if that's 35degC max during actual game play. It would be far higher than that. It sounds like you are reporting IDLE temp.
I really can't understand why you'd have a problem though. I'm very surprised that games would run noticeably slower.
Have you gone back into the BIOS to confirm your PC didn't have issues and downclock you?