Sorry, I am of no help on the first question, not sure what the ideal air/fuel ratio is.
I raced one race on my 700XX, and I only got about 15 mpg with it. Motor only had a full exhaust, PC3, Uni filter, no lid, and a stage 3 Hot Cam. I would guess I get around 25 or so while just out riding, not really sure since I have no way to detemine actual mileage. During the race was easy, I knew how long the laps were, how many I did, how much fuel I brought with me, and how much fuel I brought home, so I feel 15 mpg is pretty accurate under race conditions.
Doug