I would probably run 4.88's if you have a torquey 351W or stroker based motor, as that puts you at about 2200 RPM at 70 MPH in OD. There's not much difference between 4.88's and 5.13's...about 100 RPM or 5%, so those would work just as well IMO.
If you're rocking a 289/302, I would probably go 5.38's.
Once I get my rig back up and running, it will be 351W/NV4500/Atlas 3.8/4.88's/37" tires that measure about 36.5", so I should have more input to provide then as to whether I wish I'd gone deeper on the gears or not.