What are you guys running for oil line size? Mine are 8AN or 1/2". That seems to be the same size as what I've seen on everything up an HP500. I am thinking of going to 10AN lines when I go the the larger cooler. Do you think it makes enough difference in flow to affect the oil temp? I also changed to a 30psi bypass valve to make sure as much oil as possible goes through the cooler but, the oil is still getting hot enough to affect the pressure at idle after a mild run. I am running Mobil 1 15W50. I would hate to put in the larger cooler and then find out that the oil still is not cooling because of the 8AN lines.

8 seems too small to me. Ive never used less than 10 or 5/8" ID. Of course the fittings are 1/2" pipe so the restriction is there.

I'm planning on installing bigger oil coolers this winter. I will be leaving the stock ones in place. Even if you use 2 stock ones I think the total surface area available for heat transfer would probably be greater than a single large cooler.

The only problem I can see with using two coolers would be excessive restriction in the oil lines caused by the extra fittings. Otherwise it will probably work. The oil line restriction may not be a problem, just something to consider.