The pr3's came in usdm b16's and first gen jdm b16's. The p30's only came in second gen jdm b16's. The reason that the b16 pistons give you a higher comp ratio is because the b16's have a lower compression height compared to the b18 blocks. When you put them in a b18, the higher comp height bumps the compression up higher than you'd get in a b16 block. The pr3's will put you at around 11.5:1 and the p30's will get you up in the 12:1-12.5:1 range. You can run 12.5:1 compression on 93oct without and problems. It will give you the most HP/TRQ on 93oct. I ran 12.5:1 on a lsV about 5yrs ago and made 214whp with CTR cams and a P&P b16 head. It was a sweet NA setup. Pegged rev limit from a roll in 1st once vtak cracked at 4400, with 205/50/15's. Also, running the highest comp that you can still run 93oct allows you to get a race gas tune and get another 10-15whp whenever you put race gas in your tank and just swap the pump gas chip with the race gas chip.