In reply to PPP:
Mell Trail around kinglas reservoir at Brig O Turk ( I always walked the first hill on the tarmac as its too steep without warming up) , about 15 miles on land rover track but up to 600m.
If you've a running partner or cars both ends Loch Chon to Inversnaid, easier to run in that direction as you don't have the steep ascent from Loch Lomond ,about half marathon.
Ben Venue from Ledard
Ben Lomond from Rowardennan
The Cobbler from Succoth/Arrochar/Tarbet depending how warmed up you want to be for the first climb.