+25mv switches should be used under extreme loads and your voltage is at 1.4v or higher. These are meant for vdroop, not standard overclocking. If you are willing to slam massive voltage through it, then you need to keep the voltage from "drooping" under load, so you enable the switches which keeps it more consistent. That comes from the "professional" overclockers.

If you want to use voltage, try the classified voltage tool. It can be found on overclock.net under the classified/kingpin official forum. It will keep the voltage steady during Benchmarks and won't down clock while at idle, so you need to reset it to auto when you are done or restart the pc. The tool can take voltage to 1.3 or 1.4v, but I am not sure which. This would allow you to get to 1.45v but on air, you are risking extremely high Temps.

To use them, you would turn protection off and voltage on.

Maxwell architecture simply doesn't like voltage, unless the core temperature is well below 0c and stays there. I can't explain why, but it just doesn't like it.

60-65 seems to be a weird limit, but common for the kingpin. It's another anomaly I can't explain. If you have a small air conditioner, use it to blow ice cold air into the case. That will give you a little more play room hopefully.

Lots of fans don't lower temps, and the 900d is known for not having the best air flow.

You can try the v6 and v7 bios that Vince made and loaded to the Kingpincooling forums. Those were supposed to be the best two for air overclocking. You may find that you are at the limit though, so you you may need to figure out how to get the full load temps in the lower 50's. Under full watercooling, the temps never went over 45, and they ran wonderful.