The significant differences between a C172N and a P are as follows
1) engine: N has a lycoming O320 H2AD vs P with a O320 D2J, but both are rated at the same 160 hp
2) GTOW: N gross weight is 2300 lbs vs 2400 for the P
3) Maximum flap: N flaps go to 40 deg vs only a maximum of 30 deg on the P
All performance charts for an N will work on a P if the aircraft weight is at or below 2300 lbs. The only difference is the short field landing distance figures for the N are predicted on the full 40 deg being available and so the P will require slightly longer distances. However IMO if the the field lenght is so close to the numbers that this becomes significant than I would suggest one should not be attempting the landing in the first place ( BTW, I tell my students that book landing and takeoff should be increased by 50% for actual use)