In reply to girlymonkey:
You could link Glen Ample to Glen Artney - start in Callander and head up the railway line to the Ben Ledi car park, onto the main road for a few miles then up the forest path (only bit of hike & bike) over to Glen Ample. South Loch Earn Road past Dundurn to Comrie, then up the Glen Artney road to the pass over to Braeleny farm and back to Callander. ~40 miles, one tricky river crossing, took me 8hrs inc cafe stops, not racing. Fair proportion of tarmac but nice scenery.
Could also do Aberfoyle to Inversnaid: Head out the forest track to Duchray Castle from Aberfoyle, and follow it all the way up the Duchray Water and over the pass to Cailness on Loch Lomond (burly descent), then up the WHW to Inversnaid (bit of hike & bike) and back over the pass to Stronachlacher, either by road or by the tracks south of Loch Chon and Loch Ard. ~35miles, mostly on forest tracks. Might have taken me around 6hrs in the snow last winter. Optional variation is to return southabout via WHW to Balmaha and over the old Drymen / Gartocharn road, not done that yet.
Edit: The old drove road from Brig o' Turk to Balquhidder is also fun. From Callander west along the Sustrans route south of Loch Venachar to Brig o' Turk, then north up Glen Finglas and over the pass to Ballimore farm (hike-a-bike and bog bashing, but still fun). Return by the back road to Strathyre and Sustrans route down Loch Lubnaig. ~33miles and feels quite wild, might have been around 6-7hrs.
Post edited at 14:10