I decided I don't want to go the Safai Tank route since I like the sleeker lines of the OEM tanks and don't want the bulk of the Supertankers since it's also my daily commuter bike. However I do want longer range from time to time on trips so I changed to 2-into-1 and the Adventure tank, 7.2 gal total, pretty good and tucked out of the way. Just right for local offroad rides, or staying within 250 miles round-trip of a gas station. However still not enough range for the long Way Up North stretches that can go 265+ mi with no fuel, and you may have to turn around and go back at times.
So... I needed to get into the 10+ gal club
Added 3 gal, now I'm at 10.2gal
(~350 mi at my worst MPG)
With locking hold-down
Need to go farther? Add Rotopax extension then add another 2 gal, 12.2gal
(~430 mi at my worst MPG)
or any combination of Rotopax tanks. Allows using my hard panniers or my soft Wolfman panniers set. If I don't plan to go 2-up I can move the Rotopax mount another 6" father forward for better balance. 10 minute swap to my commuter Givi top case.