How much cooling assistance from an oil cooler

Not really....due to the fact that MOST oil coolers though NOT ALL use the cooling system (read radiator) as the cooling fluid for the oil. You could look around for an oil to air cooler, mount it in front of your radiator, or some place else where you could get air flow thru it.........however there is not that much oil in the sump, nor does it circulate that fast to carry that much excess heat off. Oil coolers are meant to stabilize the temperature of the oil.

What do you run for a thermostat, and what temp does the engine run at? What are you running for a radiator? 375hp should pose not issues on a stock cooling system IF it is in GOOD order.