Hi.  Since this is a shorter board than what you used to use, it makes sense that it will FEEL shorter.  The waist width of 25.2 is a little on the wide end of the spectrum for a boot size 9, so I assume it will be for more softer snow conditions (I noticed you mentioned powder snow in your post as well).  You will loose a little float at lower speeds due to the 4cm loss in overall length, but if this board is wider than your old 161, then it may not be that big a loss at all.

The Magne Traction is a really nice board although I have never had the pleasure of riding it.  I would think that if you live where there is a lot of newer and softer snow and plenty of steeps -- somewhere like Utah -- and you want a nice powder board that can rip in freestyle as well, this board may work  for you.  If you plan on mainly harder snowpack and if you get powder on flatter runs, the board may not offer you the float you want to keep up speed and on top the snow; then you would want a little longer like 161cm and certainly no wider.