If you stay with 4.10 gearing and 38's and do much serious technical wheeling you will regret it. There's a reason that most (unlike cerial) go deeper gears with taller tires.
I've never bothered to calculate final drive ratio as much as knowing what works by usage and observation. Regarless of the ratio of your tranny 1st gear, it seems that transfer case and axle ratios come more into play in the real world.
GLFWDA member since 1979.
Member Southern Michigan Rock Crawlers.