Powder ski width

Are you keeping the 100mm skis? What are they? Are there particular skis or style of skis you're looking at?

115-120 is the sweet spot for a pow ski IMO.

Just a look at what pow skis people are talking about a lot now will help answer your question.
Moment Wildcats (116mm), ON3P Jeffrey 116 (and Woodsman, BG etc.), ARV 116, Catamaran (120mm), Chetler (120mm), etc.

Lots seem to like that 116 dimension - with rocker/camber profiles and taper getting dialed you don't need to go as wide as you used to.
I'd say it's more about the other characteristics of the skis (flex profile, how far back the mount is, full twin, etc.) that will help you pick your winner. They're all gonna float.

Ski waist width is only one of the few things to take into account.
And only really affects how much you float, please excuse my factual comment it may not have been what you wanted to hear.

KevskiThey're all gonna float.

As wide as possible, can’t go wrong

I ski a 186 4frnt EHP most of the time. If in doubt, it is the ski I take out. I ski about 40 days a year, most of them at Mammoth where there is lots of windbuff. The EHP was discontinued years ago, but I liked it so much I bought an extra pair. In bad year I will ski the EHP about half the time and a 100 underfoot ski the other half.

What I really like about the EHP is that it has some rocker, but not TOO much. This means that If I am skiing something like Philippe's, and all the snow has slid, which happens on that line, I can make technical turns on firm terrain without too much worry. It is a great all-around ski. Skis with too much rocker can be tough to set an edge on, sometimes they want to be slashed more than driven with the shin. I like to slash and slarve, but I also like a ski that can be driven. I really think 116 is a great sweet spot if the rocker is right. Some people like skis with more rocker.

I actually also have a pair of Armada JJ's that I got because one of my wife's friends had her husband die (RIP). I like the JJs, but they have a bit more rocker than the EHPs and it is a different feel. You can't drive the JJs quite as much as the EHPs. They are still a great ski, but I have to adjust when I ski them. I am not sure if I am going to keep the JJs, I bought them because the woman wanted to get rid of them.

Elements like rocker and taper can significantly change the way a ski feels. If you want an everyday feel, like me, I would go with a 115 ski with SOME rocker, but not too much. If it is going to be more of a pow ski then you can go with more rocker.

I think the widest ski I ever skied was the old Armada ARG. It was wider underfoot than at the tip and tail, like the Spatula. I skied them on a thigh deep blower pow storm day on chair 22 at Mammoth and loved them, but they were not as fun when things started to get tracked out, and I would not want to ski a steep chute where the snow has slid on them. They would be a GREAT quiver ski.

I do think 115 or so is a great width though. I bought my EHPs thinking they would only be for pow days or the days a few days after things cleared, that they would not be everyday skis. I ski them more often than not now, unless it is REALLY firm they are a great option.