Or, start via the Mamores/Grey Corries/Kinlochleven aiming for Loch Ossian. Skirt Ben Alder, spin along Loch Ericht to Dalwhinnie. Nip over the A9, up Allt Corie Chuaich, then into the Gaick (with a bit of hike-a-bike). Descend Glen Tromie, Chomraig or Feshie into Inschriach, then cruise through the forest to Loch an Eilein (etc). Bits of this are classics, and there are plenty of options to get you started and finished. Some of the links may be purgatory. Although its probably short of 80 miles and stays low most of the way, it'd be two hard days in good conditions for most people.
Better than a day round Aviemore and Fort William, dunno, depends what you're into. Worth a try though.