In reply to Ann S:
For either Fionn Buttress or Wisdom Buttress, use a mountain bike for the approach. There's a good hard track more than half the distance, at least until you start to lose height. Ignore the "no mountain bikes' sign on the gate, if it's still there - the path was paid for by public money, for the stalkers bringing deer carcasses out on the back of hill ponies. A mountain bike certainly causes a lot less damage than a laden pony!
Some folk even nip in and out for the day, though I've always stopped in the bothy to make the best of the long approach. Something in the order of 4 hours approach to Carn Mor if walking, maybe half hour less for Beinn Lair. Fastest approach to both would be taking a kayak or canoe over Loch Maree, then directly over the bealach, if that is an option?
Rock on the former route is lovely Lewisian gneiss, wasn't so impressed with the hornblende schist on Wisdom Buttress.