Which oil pump

More damaging than the hp loss is the heat. Oil as as much of a cooling agent as the water system. What I've read is about 5-10hp more lost beyond 70psi. Thats above and beyond the parasitic draw of the usual below 70psi. There is no reason to use a HV pump unless the clearances are set up loose such as an endurance or high rpm engine. That being more than .0025" on the mains and .003 on the rods. Even then, unless it's running up past 7K there's little reason to use one.