> is that stock oil cooler/heat exchanger get the heat from the coolant or
> cooling the oil via the coolant?

I can contribute a data point on the stock 2.1 oil cooler. One day this past summer I had the cooler off my engine, so I ran my Syncro around the same course on the same day, with and without the cooler installed. Temperature outside was roughly 80F (27C) and the route I drove was long enough to get the oil fully warmed up (about 30 minutes).

Without the cooler my oil temp peaked at 230F. The second run with cooler installed showed 215F. I did notice the oil warmed faster with the cooler installed, but didn't make any measurements on that aspect.

Angus