Think of moving the spring from low to high as changing the shift points in a regular automotive automatic transmission. When you have the spring in the lowest hole, it has the least amount of tension and therefore, "shifts" sooner. If it were moved to the "high" hole, it would not begin "shifting" until the engine was revving a higher RPM. What RPM is that? No way of knowing without trying. I really doubt you'd ever get more top speed, but by putting the spring in the highest hole, you might be able to take atvantage of the engines torque for more time before it began to change ratios, meaning you might get to top speed a little quicker... always good! This might be a trial and error type of deal. Porsche930dude is right though, that little hub IS under tension, so be careful to hold the hub while removing it and take note of how much and in which direction it wants to turn as spring tension is released.