Mosc is right. When you read that octane booster raises your octane by 10 points, that means 10% of one grade higher in octane (meaning 91 becomes 91.1). It's a waste of money, but depending on your altitude it's not necessary to have 91. I would also explain this as the reason you aren't hitting what you expect for target boost, although I don't know what your actual elevation is. Even with the HWG map on my old 02 it couldn't ever achieve target boost. I would be pretty satisfied if I were even pulling close to what you're getting now, but I was hitting around 12 in the first 2 gears, then 3rd would get me to almost 14, and I'd get about 14.7 max in 4th and 5th. That was at stage 2 with a catless dp, 3 in cat-back, and an AP. No other mods.