When you're going uphill on skis, weight makes a difference - every gram counts. Going downhill wide skis, stiff boots and safe-release bindings make life much easier, but weigh more. Somewhere, there's a perfect compromise between uphill/downhill performance!
An interesting start point is to think about summer gear. A summer Alpine boot and crampon weigh about 1.3kg, so that's the extra load on each foot when cramponning up snow.
A sensible lightweight skitouring set-up (boot, binding, ski and skin) weighs more than double!
(Scarpa Alien, Plum WEPA, Dynafit Cho Oyu 88mm ski + skin)
That's quite a light set-up and is harder work on the descent unless the snow is good. You'll get much more ski performance from a bigger ski and stiffer boot like the Dynafit Hoji, K2 Wayback 96 +skin, Plum Pika weighed here...but at almost 3xsummer boot weight!
The K2 Wayback is a great ski but still definitely in the touring range. A more "Freeride" ski like the Black Crows Navis 102mm (plus Dynafit Hoji, Plum Guide, skin) takes the total to a nice, round 4kg which really doesn't help if you want to "aller plus loin".
Big skis need bigger boots like the Salomon Shift 130...a "lightweight" stiff boot. Here, with the Black Crows Navis/Plum Guide/skin.
Add a Salomon shift binding for extra security and downhill performance...and the uphill will feel much further than it should. (Black Crows Navis/Salomon Shift Pro 130)
Or go the whole way with a stiff boot, Shift binding, and a 112 Blizzard Rustler. We've almost reached 5kg! (And that's a skin, not a green leg, in the boot!)
Now, if the old adage about "a pound on the foot is worth 5 on the back" is true, then swapping the Alien/Cho Oyu/WEPA set-up for the Shift Pro 130/Shift/Rustler set-up is like putting 10.6kg in your rucksack!
