With the PC Dual-Action Polisher...the speeds go from 0-6. For swirl removal, I like 5.0-5.5... For applying polishes, maybe a step down, 4.0-4.5.
If you're talking about a circular polisher, which Porter Cable also makes. That is adjustable to specific RPM speeds... Usually 1500+ for compounding, 1000-1300 for polishing.