The Mt-Bike of XC Skiing...
...is a ski set-up consisting of:
*touring boots with a pivoting hardshell cuff -- like Alpina ST-30 boots
*60mm wide midlengths with sidecut -- like Rossignol EVO Tour
*Profil or NNN touring bindings
*intro carbon poles with big baskets -- like , uh... they don't exist -- so buy some $100 poles and have the ski-tech rummage around for big solid "scoop" 80's style yellow racing baskets under the counter -- not a round old-style tour basket, that's silly. A *light* pole is a wonderful thing. And it's TOUGH. I've thrashed mine for 20 yrs now. Just don't fall against them. When you crash, think "Save the poles!" No sweat! :) (The first time I used carbon poles I broke one in a half hour by bumping my knee against it under tension. I haven't broken one since. Knock-knock!)
Anyway, that's a rig that'll open up the tasty singletrack to you. Fast, sporty and nimble on technical trails that cover the miles. Basically any hiking trail is your oyster.
If you want to "underbike" and get a lot more over-the-ground speed, then go full-length. That'll be like a 'cross bike for ya in comparison. It'll still handle good in the tricky stuff, just not quite as robustly as yer mtbike.
Always remember that a nowax pattern is slower. In cold weather primo "blue wax" fresh snow conditions it might also slip annoyingly -- 10-20F. Waxable skis are offered over the whole range of function: giving quite a bit more speed and in "best conditions" better grip, too -- and grip makes the XC world go 'round. But for warmer weather and older snow, nowax makes life simple. Moreover, if a trail has a lot of up'n'down and you're side-stepping and herringboning a lot as it is (then plummeting down the other side) you won't notice any loss of grip'n'glide, so nowax is groovy.
To take the next step up in terms of intensity and stoutness, but without much loss of speed, go for a NNN-BC binding and boot. (Salomon has/had the rare X-Adventure Raid BC binding. Probably don't go there.) Same ski, same pole. This boot and binding will give you monster control in wicked terrain while hardly impeding your glide.
Next step up, go with a wider ski, like an EVO Track (68mm). This will turn better in steeper terrain and float more in diverse snowpack. ...Now your flatland speed and glide starts to suffer, though.
Next step up, add a metal edge (a la the famous Fischer E99). Your ski will still be about 68mm wide, but you'll be able to carve turns and do some light tele action and handle icy hardpack on any XC trails -- or mt-bike xc trails.
Your BC-NNN boots and bindings are still hanging in there just fine.
The next step up is lift-served, or uptrack earn-your-turns gear like the Karhu Guides and beefier boots and bindings, where you're not crossing much horizontal terrain at all. The Guides and their like do make quick work of uptracks, though. You can find a glade or a bowl and work your way across it with the sun and pack out a nifty series of switchbacks to toodle your way back uphill each run. This is a great way to go. Such skis have nowax patterns in the bottom and are light so they're easy to march your way back up the hill. Take your time. Enjoy your turns. I suppose now we're talking a ski rig that's like a Downhill Mt-Bike.