I'm surprised you're willing to sacrifice that little bit of ground clearance with those beefy leafs you run
I ran 35's for years with the same setup. The biggest problem was hitting the frame mounted spring hanger on the rear, after moving the axle back 4 inches. Trimming the mount and going to a larger tire got me within a 1/2 inch of my buddy running 35's and the stock wheel base.
My problem with tires is I don't drive much so they pretty much don't wear out as far as tread life is concerned. I have not bought a new set of tires in atleast 12 years. I have had great luck finding used stuff for pretty good deals. Another problem is few company's now make a 37 on a 15 inch wheel. Mostly what is left is made by Interco. No one I run with runs Interco tires so it's hard to get a feel about how they do. Mostly I hear horror stories about how they don't balance well or run fairly smooth on the HWY. The M16's and the Truxus MT both look like a pretty good tire.
I run 35" radials on the road and 36" bias TSL's to the trail, and both do just fine with 5.38, rocking down the interstate comfortably at 70+.
I can run 70+ on the flat with no problem. It could use a couple hundred more RPM but overall it's not to bad. I can take most of the hills around here in 4th. Climbing the Grapevine on the I-5 there is a few spots where I need 3rd
I was more worried about being overgeared and running in the upper 3K's doing 70. I guess I should look at a RPM calc.