Sorry to resurrect an old topic with my first post but I thought I might be able to contribute a little to this thread!
For routes in Scotland the Tour of the Cairngorms as linked above is a great ride, doable in 3 days if you camp/bivvy and are pretty fit. There is also the Fort William to Montrose coast to coast which is pretty popular. Another(shorter) route at around 70km circumnavigates Ben Avon and is a nice 2 days from Braemar. And there are loads of options in the Galloway forest, have a nice 90km loop from Glentrool that is another good weekend ride when done in 2 days.
Also currently working on a route following the West Highland Way, Great Glen way then onwards up to Cape Wrath but that's not going to be done till next summer so I have plenty of time to plan it!