Thank you all for your suggestions. In the end I used a mixture of @IWRATS South Deeside Road, @Id's south route combined with the railway path from the ANPR to the city centre (which is what @Frenchy and @Hankchief did last year)
I've been debating where to put the ride report. It doesn't fit in 'I had a lovely ride today'. We don't have a 'I had a Type II Fun ride today' thread, but that might be a good candidate.
I bought the ticket home from Aberdeen a week ago. During the week the weather forecast deteriorated, and by Friday it was a stiff north-easterly breeze and really quite a lot of rain.I packed what seemed like lots of clothes and food and headed out at 7pm on Friday. By the time I got to the Forth Bridge I was wearing all my clothes except the emergency down jacket. By the time I got to Inverkeithing it had started raining. By the time I got to Perth McDonalds (black coffee, muffin, hamburger since you ask) at 11pm, mesmerised by rooster tails of spray glowing in the front light I was pretty wet through and only staying warm by riding.
The rain eased off through Blairgowrie and over Glen Shee, but the wind didn't. I saw two cars the whole time, and was grateful for the quiet roads: the climb of Glenshee would be less enjoyable with busy traffic pressurising from behind. Twice blown to a standstill on the 12% last ramp at Glenshee, I admitted defeat and walked it. There was no risk of descending too fast down the northern side: the wind meant that it was necessary to pedal...
A snooze out of the drizzle in a bus shelter? near Braemar summoned up the blood to move off the (deserted, it being before 6 am) A93 on to the South Deeside Road at Balmoral. This would have been lovely except for the continuous rain. Id's route would also have been lovely except for the continuous rain. They are both great for a relaxing ride in nice weather (albeit Id's route is a bit lumpy, as they promised.) The downside to both of them, on reflection, is that they have no services, shelter or settlements to speak of. You are on your own and, if the weather is bad, there is nowhere to get out of it.
If I were to do a similar ride again I think I'd stay on the A93. It was utterly deserted at that time of day, and would have the advantage of taking the ride closer to bus shelters, shops (if open) and cafes (ditto).
Anyway, back in one piece with 163 miles on the clock having learned the lesson that just because it's been sunny and warm all week that's no reason to assume that it won't be wintry on Saturday. Lowest recorded temperature 6C, not accounting for wind chill...
Thank you again for the advice: it was really useful