No matter which polisher you purchase, to remove defects when using foam pads you want to be on the 5.6 speed range.
with the PC and the Megs you want to be on the 6 for sure, with the Griot's you can run 5-6, it definitely has more power. A couple of years ago I described it as a safe version of a rotary buffer. This is assuming you're using 5.5" thin foam pads.
See what I wrote in post #3 of this thread back in 2009 Pictures from Autogeek's Roadshow Class in Dallas, Texas - November 14th, 2009
While Nick was working on the front clip with the Flex 3403 Lightweight Rotary Buffer
, I knocked out the roof, deck-lid and the driver's side doors...
Something I noticed was as long as I held the pad flat
the new Griot's Garage Random Orbital Polisher
worked just like a rotary buffer. I couldn't stop it from rotating the pad and it was removing swirls and scratches like nobody's business and unlike a rotary buffer it was so easy to use. While Nick was down below on the 3403's low setting, I ran the ROP on the 6.0 setting. Swirled-out 1954 Mercedes-Benz
Cropped out of the above original WG TSR with a Green Kompressor Cutting Foam Pad on the GG ROP Speed Setting 6.0 After Same section only zoomed in on the Van in the reflection.
I still find myself reaching for the PC most of the time when using a DA but most of my DA work is final finishing or applying waxes by machine.
For any major correction work I'll tend to use the rotary buffer or the Flex 3401
If you get the Griot's, be sure to also get a 5" backing plate so you can use 5.5" foam buffing pads. The backing plate that comes with the Griot's polisher measure 5 3/4" in diameter across the face and it sticks out past 5.5" buffing pads so there's the risk of running the backing plate into the paint or components if you're not careful.