I did this in early May with a friend, using the An Dorus route as in your description. It was a glorious sunny day with great views, and quite a few other people on the hills. At An Dorus you suddenly get an amazing view of Loch Coruisg (as in your route description). From An Dorus we took the most direct scrambling line to the summit which is exposed on the East side in places, but there is easier ground on the left (West). The views of Sgurr Thuilm & the NW ridge of Mhadaidh were impressive, and I hope to return sometime to traverse those.
As you say, the N ridge of Ghreadaidh looks very steep from Mhadaidh but turns out to be fairly easy after the short steep climb out of An Dorus. From Ghreadaidh there is a good view back to Mhadaidh and the north part of the ridge round to Sgurr nan Gillean.
The south top of Ghreadaidh looks about the same height as the north top, so I decided to do that as well just in case it is ever promoted to the main top! It is not far but the intervening ridge is serious scrambling (mostly unavoidable). Altogether a great day.
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