I think Dan is right on. With the Toyo M/T you are only gaining 1.6 width from a 13.5 to 15.5. For what it's worth I didn't notice any difference in ride or handling going from the 37x13.5 to 38x15.5. When I'm in the market for new wheels I'll look for an 11 or 12" wheel but I plan on running these just like they are for now.
I would say def go with the 38x15.5. Not only does the stance look better on an 8" they are cheap!!! Well at least for you they are.
