For those playing along at home: Mustang Dyno's have all sorts of knobs and dials you can turn to 'Adjust For Things.' Weather/DA, drive train loss, etc. The "WCF" or "weather correction factor" number is generally bullshit, and it's pretttyyyy safe to take the "real" dyno number and add 5-10%...
Bring down them IATs baby, ECU does the rest. You're generally right. A little extra octane isn't going to hurt, and it's really really cooling. Seriously cooling. Very cold. Much big cool charged air.