At typical cruise power settings I'm only seeing about 8 - 10 degrees of Delta between hot & cold coolant on 13B.  I see more on the Renesis where the exhaust ports add more heat to the coolant.  Can't remember the exact amount but it was significant.  I see   40 - 50 degrees on oil Delta depending on power setting.

Adding more heat to the coolant with oil cooler or exhaust has surprisingly little effect on required radiator size.  This is because the higher delta T between air and coolant increases radiator efficiency.    For example, increasing water temp in by 6 degrees would only raise temp out by 2 degrees under the same coolant and air flow conditions.  For this reason, placing the oil-water heat exchanger in the engine coolant outlet (before the rad)  is the best way to go IF it gives you the required oil cooling.

Tracy