Since you have rectified the temps, you can be sure that this is not a case of thermal throttling anymore.. I used to have a AMD Phenom II X6 and it would exhibit a similar behavior upon reaching temps of 70+ C.. Aftermarket cooler and good cabinet helped a lot..
Then I switched to an i5 4690k, and had the same problems initially with windows 7.. Disabled the power profiles, hibernation, moved the pagefile to SSD and finally switched off the turbo mode too... Combination of all this helped and I did not notice any more huge fps drops...
But finally what solved the issue for good is that I moved to windows 10 few months ago and then noticed that despite having all enabled (power profiles set to balanced, turbo mode on etc..), I no longer face this issue..
I think it has something to do with programs like fraps and other monitoring tools.. Hence I'm no longer using them (fraps, msi afterburner and nvidia geforce experience) and gaming in peace..
Reseat the heat sink, I've the same cpu and I stress test various buggy applications/programs on it. It never goes over 68C. Your hsf or the mounting bracket is faulty.
If your board's VRM area is over-heating, it could possibly be throttling the CPU.
Try putting another fan aimed at the VRM area (the black square bits around the CPU socket).
If your board's VRM area is over-heating, it could possibly be throttling the CPU.
Try putting another fan aimed at the VRM area (the black square bits around the CPU socket).