I'm aware that under a stress test the 980 will draw more power than under most real world workloads but I want to be able to power it under the worst circumstances. I appreciate the breakdown with the efficiencies, definitely opened my eyes a bit.
After contacting hdplex they're planning on releasing an 800W unit powered by two of their hdplex 400W ac-dc converters in a few months, but that does reduce the space savings and the potential benefits of going with this small psu. So I'll see how I go, I may wait the 2-3 months or just buy a 650w+ sfx psu.