Without a total aero drag performance concern why not put that oil heat into the air instead of back into the water.
If you use the heater circuit for the oil coolers, it will get your oil up to temp quicker. I suspect most every engine builder will agree that is desirable. You may also get by with much shorter oil plumbing runs with oil-water.
If you run an oil-air cooler, you probably want to run a thermostat on it. Of coarse that is one more possible failure point. No free lunch!
However, with oil-water you DO need to have enough radiator capacity. I ended up putting a second radiator on one of my side vents. That along with a few other changes took care of my cooling issues. But with water cooled Turbo, 2 x waste gates, oil-water heat exchangers, 2 radiators, 2 water pumps, it is a plumbing nightmare.
Can't blame folks for taking the KISS approach.
As for needing an oil cooler, put in an oil temp gauge and see!
If you have marginal cooling, a simple oil cooler in a side vent may be all the extra help you need.