In reply to mick taylor:
It's a great route. Without checking a map 20km and 2000m+ sounds about right. Yes it's fairly tough but with an early start I think you'd find that it's fine for a long day. The terrain is not too bad, and once you're up high on the ridge running the two groups together is the natural thing to do.
If you have two days to spare and a bit more tolerance for hard work then the bigger circuit also including Beinn Fhada and Ciste Dubh is a truly brilliant walk; you've even got Camban bothy sort of half way. I make that 35km and 3870m ascent, so it's nearly twice as hard. But worth it.