I've never hired a bike (I already have a few), but there's a good bike shop in Pitlochry that hires bikes.
I mention that as you can take a great route from Pitlochry up through Braemar, Tomintoul, Granton, Cawdor to Inverness. Through the Cairngoms. Then train it back down to Pitlochry, or just ride down (there's alternatives/cycle paths all the way down the A9). You could also do some of the (light) off-road through Gaick Lodge or Bruar Lodge, back to Pitlochry.