I think I’d prefer the south approach, you could ride up Glen Derry to Derry Lodge, and it’s a great wee hike from there to the foot of Cairn A’Mhaim at least, I haven’t done the section between there and Corrour though, but I imagine the scenery would open up pretty spectacularly as you round the corner into the Lairig proper.
Keep your eyes open for somebody making really heavy going out of a relatively light small, I might be passing through en route from Blair Atholl. Would be coming through Glen Geusachan towards Corrour on Sunday if I don’t decide to descend the other way to Ruigh Aiteachain.