honestly, i think anything you get that's 94mm + will be fine.
the 2005/2006 fairly "epic" season i used a pair of 177 Mantras exclusively as my powder ski. Of course I was coming off having skied Rossi 7S's as my only ski, so going from someting in the 60s to the 90s was a big jump. I loved the Mantra in Utah and Cali, had a blast on it. It floated much better than anything else I'd been on, including the 87mm Karma I also purchased that season.
this season, what with less fluff and more gruff (ice, groomers) I found the 177 a bit short and squirrely. I picked up a pair of King Salmons (very similar dimensions, 3mm wider, and a bit stiffer, I believe). I have loved these much better and they work great as an almost every day ski and also slay ankle deep powder something fairly fierce.
that said, I also plunked down on a pair of Spatulas, which totally SLAY anything deeper than your ankle. Plus they're fun as hell. Now I know quite a few folks don't cotton to the surfy feel, preferring to dig deep and actually "feel" the powder, but for my money ($400) they are the funnest ski I own.
At any rate, the point of my post was that if you're a solid enough skier you can make do with anything in powder. It's just that some of the fatter/wider skis out there are more fun.
When I was in Colo this year most of the folks I was riding with were on mid 70 and mid 80s skis, even in fresh. I was on my 94 KS's and another rider (Brkln) was on 99mm Bros, but most folks were riding stuff well under 90mm and killing it better than me (granted a lot of the folks I was riding with were instructors, but still).
I think you can survive and enjoy powder on something 94mm - 100, easily, but the stuff over 105 and up to 136 will be hella fun if the snow is worthy.