typed a nice long reply this morning and it isn't here. Don't know what happened. I don't use much pressure or speed. I started with 8" wheels and burned through the finish on a few pieces and ruined them. I switched to 4" wheels and run them on the lathe at about 2000 rpm or less. I don't apply much abrasive, just a swipe or two. My wheels don't look anywhere near as brown as most peoples that I see. I use moderate pressure with the tripoli and a little harder with the white diamond. I find it's kind of like sandpaper. You want the abrasive to do the work.
That being said I watched a video of guys buffing guitars at the Gibson factory. They were using probably 15" wheels running pretty darned fast and put their body weight behind it. Of course they are probably using a commercial brand lacquer or maybe some other kind of finish. I do find that I can apply much more pressure on Polyeurethane finishes than lacquer although I don't really need to.