I installed a 100GB, 120Gb and a couple 160GB drives. Never went over 160GB with the 7200 RPM drives. The largest drive I have installed was a 250GB western digital 5400 RPM in a MBP C2D but i didn't have anything to compare the performace to. The others were in Macbooks and I experienced the macbook with the normal 80GB 5400 RPM models and then the 7200 RPM and it was a pretty big difference it seemed like. The rate very well could be higher in drives over 250GB, I can't say because I have no experience with those.
As far as the number of platters goes, I can't seem to find that information. I tried looking up the specs by model number of the 160GB models but it says N/A where the number of platters is listed. It is a Seagate Momentus 160GB 7200RPM, model ST9160823AS.