did this in summer about 10 years ago, and i dont remember it being too severe. we headed from dalwhinnie up to loch cuiach, then over to ruigh aiteachain bohty in glenfeshie, then over to white bridge, linn of tea, road to braemar.
the bit from loch cuiche to glenfeshie i cant remember that well but form looking at the os map i guess we just heather hopped, probably to "bhran cottage" kind of area so that part might be really sketchy, maybe heading north then down into glenfeshie via inschriach would be a better winter bet.
path from ruigh aiteachain to white bridge/linn of dee was alright though, boggy singletrack for a bit then mainly landy tracks.
risk wise, I cant remember if there's a handy bridge over the river feshie anywhere near ruigh aiteachain (looks like maybe from os, but maybe it was a rope/wire thing?) and i dont know if thats still a bothy (but it was quite a nice one back then)
we did it in two days as part of a coast to coast, and there's plenty sheltered camp spots IIRC, but it was a while ago, so can't promise i've remembered that well, we covered a lot of ground and drank a lot of whisky