[Accelo]

One can only get so much change from a differential gear replacement.
A 10% to 15% change will be noticeable, and a 20% to 30% change will be significant.

The motor speed with 4.11 gears and 30-inch tires is 2836 rpm.
The motor speed with 3.08 gears and 30-inch tires is 2125 rpm.
This is a 25% decrease in RPM.

However, you have lost all torque multiplication advantages, of gearing, in the process.
With an overdrive, you get a lower first gear and a 30% reduction in motor speed.
You can have your cake and eat it too.
It all depends on your wallet and skill set.
Cheers.