P55A-UD4P to video card clearance

Yeah - the whole thing is nothing but a confusing mess! The PCIe mechspec says that a x16 slot should have no component higher than, roughly, a half-inch (.543, I think) anywhere in the, roughly, twelve and a half inches of length set aside to accomodate the cards - and both ends are often screwed up: you can't count on the MOBO manufacturers to actually provide the theoretical 'clearance' area behind the slots, and you can't count on the GPU manufacturers to limit the cards themselves to the spec'd length... And, worst of all, it's becoming more and more standard operating procedure not to provide any dimensions for anything at all, much less 'Z' heights