This is probably what you're looking for.. a weight and balance Excel spread sheet for the C172
P model. Seems like the main difference between the N and P series is the Max weight. It's been supersized from 2300 lbs to 2400 lbs.
http://austingwatson.com/aviation/CH...WTBALC150M.xls
Note the Excel spreadsheet has three sheets, C150M, C172P and C150M Austin SOLO. Select the C172P sheet as per your requirements.