just my opinion, but unless the 11" are going to cost more than you want to spend, i would go with 11". You are probably right that the 9" would work fine, but if you can have better performance than why not go for it? The only problem with better-than-average brakes is if somebody is behind you and they can't stop fast enough, but depending on what's in front, who knows, better brakes may save your life someday.
"Well done is better than well said." - Benjamin Franklin (1706-1790)