I've had my 650 for about a year and a half. I'm six feet 2, about 220 pounds.
Ever since day one I've had comfort issues. I found the seat hard and uncomfortable, and the wind buffeting has been pretty crappy. I bought a touring seat, then added some memory foam to the pad. I've tried the windshield up, down, middle. I have been considering changing the windshield too.
Recently I read a post about the proper way to sit on this bike. It involves re-training yourself to use a certain posture and seating position. I tried it, and had some success, except I found I was straining my neck a bit. Then I remembered the old stock seat I had in storage. So I changed back to the stock seat. Amazing!
I'm not 100% with this yet, but I am seeing a marked improvement. The buffeting is gone, and I am able to sit on that old seat much longer than before. So, I'm starting to believe that the problem all along wasn't the bike, it was me and the way I was sitting! I still have to get used to the new posture, but it is getting better. I think I will still modify the seat a little, but to help me maintain the new position.