I've installed a small oil cooler onto my RGS rep and carried out run tests with and without it connected in circuit.
The test runs were 30miles, same road, at a steady 70mph (4000rpm), 20W/50 oil, canister oil filter.
Oil temp at start 60F (16C). Same air temp. both tests.
Without cooler, end of run, oil temperature 200F, oil pressure 10psi, oil tank very warm to touch.
With oil cooler, end of run, oil temperature 140F, oil pressure 25psi, oil tank comfortably warm to touch.
Silkolene Fuchs Oil says 200F is ok if a decent oil is used, which will maintain its characteristics without degrading, by that I'm sure they mean a recognised main stream manufacturer, eg. Silkolene Comp 4 20W/50 and not some cheapo oil.
For me, I'm happy with the increase in oil pressure, so the oil cooler stays.
Hope this is of interest.
Alan