Hi Steve, Running the polisher at a low speed is a good idea, especially on and around edges, body lines and near any openings ie. Headlight openings etc. Generally 2,000 grit paper should be fine enough, I finish my wet sanding with 2,500 or even 3,000 grit tri zac....not so much for getting rid of sand scratches but for speed and ease of polishing. I haven't Meguiar's for years and haven't used the 85 and 83 products. I use 3M's perfect it system of polishes and foam pads so it's a little difficult for me to comment on how well the Meguiar's products work.
You mentioned that you are running the polisher at a low speed...which is good, you may want to try ramping up the speed a touch...as much as you don't want to burn though, with a higher speed you will generate a little more heat and things can melt in for you easier....I'm not talking about running the polisher at full throttle, if your polisher's speed settings are from 1 to 10 and your running it at say 2...try carefully running it at 3 or 4 on large surfaces without edges openings and body lines...it should save you time and get rid of those sand scratches. Your still not going wild with polisher speed, just take care, be cautious and keep the polisher moving. Another trick is to keep the foam pad damp, damp not wet, and clean, (one reason I don't like wool pads is they are hard to keep clean and do generate more heat than I like)
The only thing I can tell you about fine paper plugging up quickly is that it is fine paper, and they will plug, single stage always seems to plug more than clear coat, keep the paper real wet and you'll get more life out of it.