Hi, I have allegedly managed to get GPU acceleration working. I had to add the card to the suported_cuda_cards file and I can select it. I did a few experiments turning MPE on/off but it does not seem to make any difference. It does however change the render bar from red.
I have the same card. It's been my experience that the GPU isn't used for everything. It's used for GPU accelerated effects, and it's used for scaling during export.
I've exported straight from a 720p Canon MXF timeline without any applied effects or scaling changes to an H.264 format and the GPU isn't used at all. All 8 CPU cores are at 100% during export.
I can do the same thing but downscale to a smaller resolution (like 240p for a smartphone) and the GPU will go to 80% (and the CPU is at 100%).