Quick answer: it will help notably if you use a 3.73 rear end with the tall tires you have. Basically the 215/85r16 should have a diameter of apx 30.5". The tires I'm using (205/75r15) have a diameter of apx 27" (all tires will vary a bit, but we can use those numbers). Your original 6.00-16 tires were 28 to 28.5 inches in diameter. I've always used 28" because it was easy to remember...16" + 6" + 6" = 28", but as I recall 28.5" is the amount the tire industry used. But the key is to compare your tire height to mine and the 3.73 to 3.07. That's where it gets interesting.
Going through the rpm/mph calculations, using 30.5" diameter tires and a 3.73 rear end with the same transmission gear chain I have (4.03, 2.37, 1.49, 1.00, .86), you will be just fine. The best news is you'll be able to stay in first gear until around 15~16 mph. And after you're through 4 gears and go in 5th, your rpms will fall back to 2100~2200 at 60 mph...which is right where I am. For contrast, however if you had my wheels/tires/transmission and the 3.73 rear end and wanted to shift at 2500 rpm, you'd be going from 1st to 2nd at 12 to 13 mph. The extra 3 mph may not seem like much, but at that speed it will make the difference between needing to shift too soon or wind your engine up another 500 rpm. But I should add I drive in city traffic...which is monumentally different than traffic in a small town or village.
I need to do Lugnutz’s suggested procedure to verify gearing of my t5.
