My 06 YZ450F is due for a piston change (probably has at least 100 hours on the motor, but is running fine), so I thought I would put in a high-comp piston. I want to get a CP, and they make a 13:1 and a 13.5:1. I don't mind running high-octane fuel, but there are times where it is very inconvenient to get it (the closet 100-octane pump is about 60 miles away). I searched this forum and it seems there is a variety of opinions on whether 91-octane will work OK with a 13.5:1 piston. What is the real story?