In terms of durability I would lean toward the Armada line. Some of this years pow skis have a textured top sheet which resembles an old pair of Head mojo 80s I use to have which were possibly the most durable ski I have ever owned. I have owned 3 pairs of Armadas and they have all held up excellent over the years.
Personally if I were in your shoes I would not consider the Magic J, It looks like a great deep pow ski but for the big mountain you sound as though you will be into it seems a bit overkill (140 underfoot is enormous). I skied on my regular JJs during the 10/11 winter at squaw where we got 810" and they handled pow that was nearly as deep as I am tall on a regular basis without any issue what so ever, 115-120 underfoot is more than enough.
Besides what is the fun of skiing pow if you are on a ski that just sits on top of it and doesn't even allow you to sink in let alone face shots? It seems as though the mentality of the "true Pow ski" now-a-days is to overcome the powder, rather than actually shred/enjoy it!
Bottom line is get something you will be comfortable with and will allow you to ENJOY/SHRED the pow, and don't worry about being able to float, save you money and work on your technique and you will have a way better time than you would floating on top of the snow, not knowing the difference between 4 inches and 4 feet.