I really should look into this octane thing, I've heard about it but I've never actually seen it. I ran GPU-Z during a render and my PerfCap is showing a solid VRel bar which puzzles me, my PSU is a modular, and I have each of the power connections to the card on its own cable so voltage should be steady?

GPU-z during the render of 'duel' about halfway through And this is GPU-z after the render had finished

I downloaded the blender benchmarker, did a quick bench which rendered bmw27 and classroom.

My results were :

bmw27 - 109 seconds [average 343]

classroom - 257 seconds [average 1053]

Averages taken from this page - https://opendata.blender.org/query/time-per-scene