I'm not sure who BMW made the F/G650GS (single) seats for, but they weren't human. I first had a '99 F650 and now have an "03 F650GS. I couldn't go 50 miles on the stock seat without having to stand, a lot. A Corbin fixed the problem for me. Between the 2 650s I now have over 88,000 miles with my longest being 3 Alaskan rides, from South Dakota. Get an aftermarket seat and you will have a new riding experience.
I just picked up a sweet 03 F650 CS how different is my seat than the GS. I am 6', 225 and this stock seat is nice. Also looking for a good place to get a larger wind screen.