I went 4 miles last weekend, and then yesterday i went 17 miles on the Meal Circuit at brig of Turk, so im about ready for the Ht550 now

I do have a holiday coming up in 2 weeks time, and im looking for a route to do over 3 or 4 nights.
Requirements are offroad, but nothing too steep/sore on the legs.
I quite fancy the cairngorms, and from looking at the Cairngorm Loop route i have a rough idea of a route. Cant quite work my mapping program properly, but it seems about 80 miles or so.
From Blair Atholl, up the cycle route and turn right at Dalnacardoch lodge, heading towards Gaick Lodge.
Into Glen Tromie, right at the tromie bridge over to Glen Fesh, heading to Bynack Lodge.
Then from Bynack, either down Glen tilt to blair atholl, which looks the easiest, or over to Glen Fearnach and then back towards Blair Atholl.
Anybody that knows the area can tell me how easy/hard a route this would be? Relative to each persons fitness i suppose, but try judge the hardness based on someone that still gets a sore arse from sitting on a bike seat and has dodgy legs at times

Also open to other routes, in diffrent areas, if anyone has any better suggestions. Just looking to go about 80-100 miles on relativly good tracks/gradients.