I once climbed Muir in January. We parked at the "Road Closed" sign and skied almost to Trail Camp the first day. It snowed 6" - 12" that night, so the slog up the slope to the right of the switchbacks was brutal. My partner turned around, and I tagged Muir (with 12" of fresh snow on it) by myself. We skied out that afternoon, reaching our truck in the moonlight.
We had originally planned to climb Whitney, so we came back in early March to finish the job. We more-or-less followed the trail except for bypassing the switchbacks, camping one night at Trail Camp. We skied from the summit to the "Road Closed" sign, but the heavy packs and breakable crust made for an unpleasant ski.
I also did a solo winter climb on Russell in mid March (a different year). I brought snowshoes and never used them.
Last year, I did Whitney, Muir, and Russell as a three-day trip in late April. I didn't bring snowshoes or skis. There were times when they would have been useful, but they wouldn't have been worth the weight.
If I were doing Whitney again in early season, I would take the MR.
