I've ridden this route a few times and i think the 1st time was with Rick many moons ago! It's a temendous route, and the downhill is superb. Another good starting place however is Durisdeer, as the downhill back into Durisdeer is also excellent. Though last time i did it, it was on my Cannondale SM500, so no discs and no suspension!!! Arms were killing me afterwards! If any one is interested in doing some loops in this area then let me know as I've ridden most of the tracks in the Leadhills and surrounding area.
It's definitely an all day outing, and reckon on about 45 miles of tough off road terrain. You can also use quite a bit of the Southern Upland way as it cuts through that area as well.
Greig.