My G5, now 9 weeks old and with 2400 miles on the clock very occasionally starts to fade at idle but a very slight twist brings it back up. I have noticed lately when I get back after a couple of hours riding it's idling a little on the fast side.
The engine felt a lot less lumpy and a lot more eager after a few hundred miles, and more so after around fifteen hundred. It purrs along nicely at around fifty-five to sixty, and doesn't mind seventy at all. The bike vibrates a bit of course, but only begins to get shaky at seventy and up.
This is a G5 not a C5. I rode a C5 for a week or so, and it wasn't nearly as smooth as mine. It was the demo bike so probably hadn't been babied much, but still it had less than a hundred miles on the clock. Don't know if there is generally a difference between the two models.
A bit more poke going uphill would be nice, instead of having to occupy the slow truck lane.....