If you are looking to buy just one ski, go for the madshush 78 or s-bound 112. Those provide the bare minimum amount of flotation needed for powder. Even then, you may find that you can barely move on the deepest days. The inner mountain west gets dry, fluffy, deep powder but it doesn't take long for it to consolidate between storms.
Unfortunately, XC cambered skis are bad on firm snow and that gets seriously exacerbated as they get wider. The madsush 78 is terrifying on firm snow. S-bound 112 might be better. It's also very hard to edge a wider ski in leather boots on firm snow. The boots just don't have the leverage.
You can do a wider downhill oriented ski with plastic boots as a one ski quiver, but if you are going for XCD skis and leathers it's not really possible to do one ski for all conditions. You need a ski for firm and a wide for powder. Fortunately, used XCD skis can be inexpensive and it shouldn't be too hard to find one narrow and one wide pair of XCD skis for a good deal.