I think its a great idea. A lot of the larger displacement 4 strokes had the oil cooler from the factory, including the 350x for example. The oil cooler does make a difference in the overall temp of the engine, providing better performance, because of a cooler engine. I have noticed power loss riding a 200x on a hot summer day, especially when going up a sand hill with the throttle pinned. It performed much better a week before, when it was 70 degrees. A lot of the racers back in the day ran oil coolers, especially on 200x, so that must mean something.
THE 80's RAGE! Currently owns:
81, 85 Yamaha Tri Moto 125
83 Yamaha Tri Moto 200 x2
82,83 Yamaha Tri Moto 175 project
85 Yamaha Tri Z 250
84 Kawasaki Tecate 250
84 Honda ATC 70
85 Honda ATC 350X
84 Honda ATC 250R
(2) 84 Honda ATC 200x
82, 83 Honda ATC 185s
81 ATC 200
Lots of other parts and bikes