My favourite mountain bike route. I usually do it the other way round though.
Good luck in France.
Was going to do it the other way round as that was the way I'd done it before, many New Years ago. But the guy in the bike shop recommended the other direction, and I think I probably agree. The descent from Ryvoan Pass is stunning, and doing the Rothiemurchus section downhill was some of the most picturesque and enjoyable biking I've ever done.