Weird result. I guess it makes sense that it could use twice as much CPU to finish in half the time but looking at the numbers doesn't feel intuitive.
I wonder how many shaders this would keep busy. There is probably a class of GPUs and above that this could work on rather well alongside an already large workload.
2x e5-2667 v2: real 0m2.217s user 0m56.088s sys 0m0.016s
Seems like it's pretty inefficient with the dual CPU setup.