2 speed, 3 speed, 4 speed all have the same final drive gear: 1 to 1, and have no effect on top speed or any speed in high gear. Only overdrive, or an overdrive transmission (T5, 700-R4) does this.
The axle will only help if it has a numerically lower ratio than yours, such as 3.55 vs. your 4.11, etc.
What is it?
