The temperatures are exactly the same where the GPU temp caps out at ~68. However the gpu fan speed is lowered by a fraction.
I've put the logs up here.
All in all, it does very little.
Turns out a 40mm fan fits nicely at the back of the case above the GPU.
A 40x20mm Noctua fan means it's near silent and it does a really good job of pushing air.
I cut it out using a holesaw, and cleaned up using a Dremel to get rid of the rough edges. A little black paint helped cover it up...
Mine didn't make it into the competition, but I'm super proud of how it turned out.
The other WOODAN case in the contest got my top vote. Looks very nice. I'd love to know how they approached cutting the holes in the vinyl. My method was a lot of Netflix and a thin filing tool :)