I asked the same question a few years ago and was told by a reliable source that the difference is minimal at best.
Not sure this will help answer your question very well, but just for your info, I run very large oil coolers with Kieth Eickert oil thermostats. By the looks of my coolers, the oil runs from one end to the other and then actually turns around and runs back the other way through another channel/passage ALL within the cooler itself. However, the water only seems to flow through one passage and only in one direction. I didn't know this until I actually took apart the cooler just to check it out, clean it, and inspect for any obstructions.
Thanks so much. Now that I know the name I was able to find much more info on Google.