I have always gotten around 10 miles per gallon but always figure 9 to make sure I have extra. At the MORE 500 I ran way short and we came to later find that we were down to 7mpg, then installed a fuel regulator and was exactly at 10mpg once again.
My wife won Ridgecrest in her 11 car a few years ago and we guessed 10mpg for the first 3-4 races she ran. She finished the race and we decided to pump out the cell, the elec pump went @ 30 secs and it was over with about 3-4 cups in the dump can... We figured we'd finish with @ a 4-5 gal buffer. Moral of the story: We were actually getting @ 7.5-8 with a single port 9 car motor and just got lucky for the first few races as we over planned her fuel stops. Don't figure that because "Billy" is getting 10 that you'll get 10 as driving style, the vehicle etc... do play a factor and they are not the same.