With my 7970s on their last day in Windows, I decided to bump up to 4 tasks on each GPU.
Running 4 tasks is definitely more efficient than two tasks, and I am averaging about 1:30 per task. Overall CPU usage never goes above 29%, but individual cpu/thread usage will bump up to 98%. Looks like I can still run CPU tasks alongside MilkyWay, as long as I set affinity, to make sure that the CPU tasks don't hit the GPU threads.
*Edit* After setting affinity and limiting Asteroids to 8 tasks, everything looks stable and the run-times on the GPU tasks are consistently at 1:27-1:33 per task.
Well he's Claiming he's running 4x.....