. . . the tank has taken over 6 gallons on many occassions.
I would take that up with your local wieghts and measurement people. It sounds like your gas station is ripping you off!
The touring model tank only holds 5.89 gallons.
I've put in as much as 5.69 gal. With the mileage I got, I figure I only had about another 6 miles to go before I would have been pushing. Computer already read "0" miles to empty 10 miles before the gas station.
The computer isn't completely useless, but it's close. The light comes on at about 1/3 of a tank (seems early to me). And when the trip computer first says 0 miles left, I calculate that there is about 0.5 gallons remaining. The gas gauge seems roughly accurate for 3/4 to full. Grossly in-acurate from 1/4 to 3/4, and accurate again below 1/4. When it says 1/3 full, it is at about 1/2. For the most part, it is pretty consistent, so once you get used to doing the mental conversions you know where you stand.
I find that higher altitude, cooler temps, and dryer air all seem to improve the MPG. Best I ever got was once during my 1st 10k. I got 56MPG (8k feet, cool air - but I wasn't babying the throttle since we were outrunning rain clouds). I never saw it again.
During my first 10k the bike got low to mid 40's. After the service, it dropped 5-7MPG (step change - not gradual). I asked the shop what they could have done to affect it so much, but they couldn't think of anything. Now I get 34-37MPG depending on whether or not I decide to let the other bikes I'm travelling with keep up or not.
I don't generally cruise at more than 85MPH. But I do enjoy carving up some twisties. On a 2 lane highway I always pass wide open throttle, but that usually only takes a few seconds at a time.