http://www.langdalecharityfolkfestival.co.uk/ (September Festival Sept.9-10-11 2011) is a great week-end (whatever the weather - and the May w/e had 100mph gales blasting down the valley) but may be a bit out of your way. Langdale is not quite a cul-de-sac, but routes north from there are mountainous, to say the least! And it's a way back to the A6. But if you can contemplate the Rob Roy Challenge AND ceilidh the night away, you might easily fit Langdale into your itinerary. (I lived in Aberfoyle for a few years and got to know the hills around there fairly well).
Ross