For brass prep, I just run whatever I have that need to be processed (200-1,000).
For loading, it depends on the cartridge. For standard cases, I'll load 300-1,000 at a time. For oddball wildcats, it' s usually just 100 at a time (since it's done on a single stage press).
All of my bulk processing is done either on a Dillon 750 (for loading) or Dillon CP2000 (for case processing).
The exception to this is 300 BO case forming. When I do that, I'll process 1,000-2,000 in a sitting. I figure if I have to set up the case trimmer and shop vac (for sucking the brass chips out of the die), I may as well process an entire 5 gal bucket of brass. It's loud, but I can salt away enough cases that I don't have to worry about making 300BO from .223 for another year or so.
Both of my Dillon's are on Autodrives, so once the machines have been set up and adjusted, I just let them rip, and keep feeding cases into the hopper. For loading the biggest drag is keeping the primer topped off, everything else has an automated feeder.