Most polishes will have a recommended speed range on the bottle. Most of the time, you'll get the best results if you stay within the polish manufacturers recommended speed range. And with some polishes, they just don't work at all unless you follow their speed guide. The 1Z pro line is notorious for that. They say 1k max speed, and they really mean it; anything faster and they flash over fast.
Start by following the recommended speeds, then make adjustments as necessary. Personally, I rarely go over 1.2k when using foam, and never over 1.8k with wool. But I'm also a whimp.
