It's not the cards, it's the CPU's
Prime is claiming .293 CPU per application, which means I could increase production by doubling up. Works on some machines and not on others. All Machines being 83xx series vishera's (except for Haf-2 which is an 81xx series and doesn't have the power to double up)
Not all CPU's are alike...
As far as the GPU I find that the AMD's are equal to the Nvideas, it is the CPU side that limits them. Intel is favored over AMD. which is always the way it has been with prime.