Wow that's a lot of gear! I'm running 37's on 4:56. But I am also running a I6 with a T-18 trans. Is that not low enough? It crawls pretty slow. I even ran 3:55s with 33 inch tires.
You would not see much difference between 5:13's and 4:56's..
5:13 will be better if you are running stock trany.. first gear takeoffs need lower diff gears unless you are running a low geared trany..
Thats why the T18 and I6 is handling the 37's at a 4:56..
My opinion! If you are going to pay to have it done! Only pay once.. don't look back saying " dang I wish I had gone lower"....
I agree with Bounty; I ran 31's with 4.88, and it was the bomb. I now have 33's and 4.88, and I am wishing I could upgrade to 5.13's... So 5.38 is defenetly where I would go for 35's, which means I would go higher (lower) for 37's...
go as deep as you can, not sure what you have for axles, but go as deep as they will allow you. for dual sport drivability (trail and street) 5.13 should be fine, you will kinda fall inbetween what is considered ideal for both uses.