I run a larger gas tank on my serval mostly because the original bike came with it. I was against it and planned on going to oem but i lacked some plastics, After riding with it i didn't even notice a difference in how it handled so left it, even though I had no real need for it since i mostly trail ride. I always find myself near the vehicles well before I am ever low on fuel. If i was a dune rider it would probably be more of an issue.
Make no mistake though, If im really hammering on her it does guzzle the fuel crazy compared to all the other bikes and quads i run with. id say roughly 3 hours of ride time.