Voltage locked by Windows?

[Potato Joe]

In my rig I have 4 GPUs, a 980 Ti, 950, 720, and OEM 620 (the relabeled 520) and I use the 620 and 720 for folding@home. The issue is actually with the 950. I can't change the core voltage and what it's set to seems to depend on how Windows feels on any given day. Sometimes it's locked at base settings, sometimes it's locked higher. My motherboard is a Gigabyte X99 SLI and I don't have the 4-pin thing at the bottom of the board plugged in (unsure if this matters). Power supply is an EVGA Supernova 850B2.

 

[nukemaster]

It may be worth connecting that plug at the bottom since Gigabyte recommends it for systems with 2 or more video cards.