You could split the Ramsay round, and stay in Achintee or, a bit further away from the hills, Spean Bridge
The southern Cairngorms are very runnable and Spittal of Glenshee, or Braemar are at either ends of a lot of high country
Bridge of Orchy is between god rounds to the East and West
In reply to Elsier: Continuing the Cairngorm theme, how about doing the Lairig Ghru run from Braemar to Aviemore and returning next day over the tops? Two blinking hard days mind you! It would be a bit shorter if you started the run from Linn of Dee and not Braemar police station which is the normal race start I think.