30% of your cooling is done by your oil
I think that's the high end, and it's not what you get - it's what's possible to get.
The problem with using oil is that even with a cooler, the hottest oil (the most efficient heat rejection in terms of radiator weight, BTU dump per inch of air exposure, degrees lost per pass, etc.) is a dry sump where hot oil from the crank goes to a filter, then the cooler, and finally back to the pressure pump.
A cooler receiving oil from the pump is probably getting "cold" oil from near the bottom, and (important point) oil doesn't circulate in the pan the way you want, unless you force it to. To get hot oil to the wet pick-up, you need baffles in a pattern that might not be helpful for your G force and windage control.
With no cooler, the oil temp loss is limited to oil washing over a radiant surface (sitting in the pan does very little). Diverting more oil to the head works since it's high temp and continuous drain-back (also increases VT life, and cools the springs), but your drains must be big enough or the oil finds the guides.
