Hiya Kowboy! Welcome to our playpen...

You asked a couple of interesting questions; and none of them have any simple answers!

Fuel mileage?? That depends solely on what your right wrist does when your brain screams , "Go!"... Most folks seem to get around 30mpg, but ihat varies quite a bit. I average about 33mpg with my RT, but i drive like an Olphart...

Comfort? At 6'4" you'll want to sit on both the GS/RS and RT models to see how they fit you... The seating position on the RT is more touring oriented, so I'm guessing that it'll give you more of a chance to spread out and get comfortable.
More than ahlf of the fun ius in the shopping anyway!