I’m pretty sure this is the Martin I know with the red GS. sorry for the late reply.
I get around 120 miles in city driving before my reserve light comes on.
I can usually get another 40 miles out of it - but I tend to fill up after about 20.
I’ve gotten over 200 miles on a tank before - on a longer distance trip with mostly highway but some city.
The stock seat for me is fine for commuting but terrible for more then 2 hours of riding out. I’m thinking I’ll keep the seat original but on my next bike (F800GS?) I’ll go for the comfort seat option from BMW - if it fits me. Might be too high.