I spent a few years cruising up and down the west coast, and Az, nevada, and Idaho, (we'll just forget about Utah ok?) on a cb350, spend almost all summer on the road roaming, only stopping long enough to work to get money to cruise some more. Hole up in the winter wherever I was when it got cold, or head back to Cal/Az. Never had any problems keeping up with anyone, and the only issues with the bike was tires.
I think a 500 would surprise you in it's staying power.
If I'd listened to the people who told me a 350 wouldn't go, I'd have never left the bay area.
The only thing is I'd want a more current bike for long trips simply in case of unforeseen problems, overnighters are nothing, my buddies and I take 5, 8, 10 hour rides all the time, my 74 cb750, Charlie's kawi 600rt ( the touring version of the ninja), Matt's suzuki, and sometimes Dave's 80 cb750, No issues other then when they want to do wheelies, and all I can do is burnouts.
Ken.