Mechanically, the R65 should do it, but I can certainly agree that 2-up it would be pretty cramped even packing light. I'm over 6 feet tall, and while it could be do-able for me to ride solo out there on it, I don't know - the concours is soo much roomier and more comfy... Knocking off a 600+ mile day on Connie with her big fairing is much easier than on the R65LS.. It may be a moot point anyway as I don't think that I'll be able to take off the 2-3 weeks that I'd want to have for making that trip to the west coast - I like taking the time to smell the roses along the way when I can.
Sue's ridden some big distances on an F650 single, and the newer F650 twin as well. I rode my LS from NH down to Gray, Tennessee to the rally in July - it was 2.5 days riding heading down and 2 days coming back. Round trip was ~ 2100 miles and it was a piece of cake, but I don't know how much further distance I'd enjoy riding a basically naked bike now that I'm over 45 and I'm not as flexible as I used to be..