stock is usually 4.10 to one.
33 inch tires to return to stock gearing ( where the speedo reflects actual speed) is 4.88 to one.
the gears that I run with 36 inch tires is 5.29.

the lowest gears available are 5.71 to one but have a rep for being weak due to pinion size.


I would say go with the 5.29s and rev it a bit higher.
with 31's and 5.29s I would (just a guess) say that 60 mph would be reading 75 on the speedo.
75 would read around 85 to 90 on the speedo.