It all depends on how you do it, but you should figure on a tank change as it relates to hitting the handle bars. Moto Guzzi has a tank around SEVEN gallons and BMW has one a tenth of a gallon more or less. I can just see filling up for $25.  

All I know is that with the tanks both full, loaded with camping gear, and then with my 180 pounds of "muscle" thrown in my Sav rides like sitting on an armchair. It's stable, steers true and doesn't seem to react to anything less than heavy duty side wind gusts from a big storm. The big trucks on the highway, passing or meeting, don't give me any problems. Part of it I'm sure is the full windshield and the heavier duty shocks on the back. The only changes I noticed are that I went a lot farther before I had to stop for gas AND that a better seat makes a difference when you choose to go those extra non-stop miles.

All that extra weight on long trips might have been the reason I needed new fork seals at 27k miles though. But when you bounce a bike this size down the road on 4k miles trips to Florida from Minnesota and back a couple times I suppose new seals aren't all that unexpected.

Jack