My girlfriend and I did quite a bit of long distance two-up touring on my 2012 DL650. She told me she was pretty comfortable on the stock seat, and had lots of room to move around. She's pretty slender, but when we had a Harley Road King, she was actually more cramped and there was a lot less space between us. The hardest thing about that bike for her (and she has the same problem as she does on my Super Tenere) is getting on and off the bike because it sits so high. She always waits until I get on the bike, they she does a Rockettes style high kick to get her leg over the pillion part of the saddle. She then slides onto her seat. I've given up trying to teach her to stand on the footpegs to get on, or at least get on first on the lower front part of the seat and slide back.
Her one complaint was when we were on the interstate and getting knocked around by the dirty air coming off all the trucks, she felt decidedly unsecure back there. I never felt that, probably because I had the bars in my hand and had a sense of control, but for some reason she would get unnerved back there. She says she doesn't get that same feeling on the S10, and that it feels more "planted" to her.
I felt that the 650 was a little underpowered on the interstate when both of us were on it with a full load of gear. That was one of the main reasons we moved on to the 1200 CC Super Tenere. Other guys never had that complaint, so it's definitely a subjective opinion. Other than that, the 650 was a great touring platform.
"No matter where you go, there you are."