Results are in for my i5-4690k:
Stock fan, no overclock (for reference)
90C @ 2 minutes. Stopped test.
Sythe Grand Kama Cross 2 fan with TIM that came with fan.
64C @ 5 minutes.
Overclocked to 4.3Ghz.
94C @ 5 minutes.
Delidded, Direct to Die with Kryonaut, 4.3Ghz overclock.
77C @ 5 minutes.
So we'll call that a 17C temp drop, even though it was a bit warmer in the room during the delidded test.
Overclocked to maximum automatic setting of 4.8Ghz and system was stable. Temps rose quickly during testing so I stopped it. I could probably lower voltages and find a stable maximum but I have no desire to find the exact limits of the system. I think I'll be good with a 4.5Ghz automatic overclock, which hit 84C after 5 minutes.