Yeah, the E ply is not the best idea for ride quality, component longevity, or fuel economy. The only E worth it is the DuraTrac and its 6-ply-rated tread is significantly thinner than any AT or MT I have seen. A lot of Jeep guys use that one. If you take a look at the DuraTrac's tread pattern and shoes, it is halfway towards a dedicated snow tire. Plus the rubber compound is slightly softer than anything I have used. It is pretty impressive on snow. While I prefer the MTR Kevlar off-road and on rocks, the DuraTrac is not far behind there either, while being lighter and better on snow and wet conditions.

I use 87 in the 4R and 91 in the Merc but only because it calls for it. Both have 4.7L V8s so sometimes, I forget and use 91 in both. I am sure 87 will be fine. I don't drive that much so 91 works.