Might be best to ask on the biking forums (Singletrack world http://singletrackworld.com/forum/forum/bike-chat are pretty good). As Alan mentions, there's quite a bit of hike-a-bike on the side of Loch Lomond - style type ladders to get over boulders, etc. The rideable bits seems to be Tyndrum onwards. No idea of the biking record but have seen c.12hrs mentioned on the STW forums.