Second the planning pause on the way down the Mhaim ridge towards Big Mac. It’s good advice to take that moment to decide how you’re going to tackle the ascent as the boulder field is tricky to negotiate and the grass area out to the right further up while it’s still steep might work better for you.
They’re both good descents in my opinion, just different.
If I was riding solo, I’d probably stick to the classic path down past the Hutchison hut and into Glen Derry, not go up the extra climb, purely from a safety perspective. On Derry Cairngorm, you’ve a far less chance of being found by random walkers if you take a nasty fall.
I still very much enjoy the classic descent, all the way down to cross the ‘closed’ little iron bridge and onward to Derry Lodge.
As for weather on the 13th, that’s the weekend of the Cateran ultra marathon so it may well be minging again..