In reply to Lynsety:
There is no logical, away from fast traffic route on the west. All W-E roads on the west coast are trunk routes with heavy traffic, yes the scenery is nice but the road environment isn't.
As a left field suggestion. Kyle to Armadale get the ferry to Mallaig, then either straight to Fort William, or go via Moidart and Ardgour to Corran and then up to the foot passenger ferry to Fort William (the latter route is much nicer and really good peddling). Get on the Train at Fort William, and get off at Rannoch station. Cycle to Pitlochry. Follow A9 cycle route to Dunkeld. Then you can work minor roads to Forfar and Montrose.