Have you ever driven up the A9 and seen cyclists grovelling into the wind and rain in that bleak section between Pitlochry and Dalwhinnie and thought “that looks like not much fun”? Well, you were right. I did that in the opposite direction last July in grim weather and there was some questioning of life choices. It’s probably lovely in the sun.
Also the cycle path wasn’t in very good nick in places and certainly not something I’d want to being doing on a proper road bike. Was fine with 35c tyres.
The bit round Aviemore was lovely though.
Dundee to Perth is quite pleasant, although someone at Sustrans has a sense of humour given it takes you up a 20% hill in the last section. Some lovely views just after that though.