There are a few different ways to overclock on the X99-Gaming 5P. The easiest way would be through the EasyTune software. You can select Auto Tuning and it will try and find the best way to overclock your system.
Of course you can click on Advanced CPU OC on the left and set your own values to overclock.
You can manually overclock using the EasyTune software or go into the BIOS and overclock yourself. We ended up with a final stable overclock of 4.4 GHz
The big question is did the OC_MODE switch really help with overclocking? While I was not able to reach a higher stable overclock with the switch in OC_MODE compared to the default mode, when in OC_MODE the system was more stable. I was able to confirm this as many of our stability tests ran just fine at 4.4 GHz while in OC Mode, but would not run at all in default mode.
As you can see it looks like 4.4 GHz is the highest overclock we have been able to achieve on the X99 platform on all of the motherboards that we have tested.