The only way I could see using this high of a compression piston with pump gas is having a big cam to bleed off some compression. Like I said before, I run 10.5:1 CP pistons(bought from raceeng.com and had them in 2 days) and I have had my head milled at least 3 times due to rebuilds/headgasket and I run 93 with no ill effect. I would suspect I'm in the area of 11:1 compression, maybe a tad shy of it(I have no way of knowing right now because I don't remember how much was taken off the head each time) but it feels good. I would say go for the 12.5:1 and just get a cam with a decent amount of overlap to bleed off the compression to run pump gas.