Let me establish two approaches to a ski traverses longer than a week, as I understand them. The classical approach is similar to a polar expedition. This expedition style entails harnessing a heavy (>1kg) sled that cannot be practically carried, taking a lot of liquid fuel, a smaller pack, and making an average progress each day of 8-40km, summing up and down. Ski tours are loops starting at basecamp when the time is right. Passable terrain is limited by the skill to handle the heavy sled, but is practically limited to mellow terrain with few obstacles. The range of total distances covered can be very high (1000km), strongly depending on conditions. Weight is always an issue but there's a sled. This approach is great for long-lived basecamps in remote places.
I will focus here on the application of alpinism's 'light and fast' style to ski traverses. I'll call them alpine style ski traverses. The key difference between expedition style and alpine style is speed. Alpine style assumes speedy sustained progress, typically twice as fast as expedition style. The choices of gear are important, as weight heavily influences speed. Training requires a solid aerobic base, upon which a lot of training with a heavy pack can be done in the off season.
Alpine style ski traverses entail carrying everthing in a large, yet light and compressible backpack, possibly with a small (<1kg) packable sled (e.g. a boggy, see http://www.johnbaldwin.ca/trip-planning-toboggan.asp) when starting. Average progress each day can vary wildly from 10km to 50km per day, summing up and down. Passable terrain is limited by each group member's ability to ski with a loaded pack. The range of distances to be covered are moderate to high (100 to 500km) between resupplies, are limited by the speed of the group and their ability to carry the sustaining food and fuel, and, of course, are strongly dependent on conditions. Weight is a core issue.
The alpine style allows access to the much steeper terrain. Thinking of forward progress in distance is not useful. I'll define an 'alpine unit' based on the military approximation, but is taught in certain German circles as a Leistungskilometer (effort kilometer). I was taught the same concept but the word Einheit (unit) was used.
The concept of an alpine unit hinges on the assumption that one kilometer of distance requires the same amount of effort and time as a hundred meters of altitude gain. The alpine unit equates 100m vertical gain with 1000m distance. A handy calculation for imperial units is difficult on the fly, so roughly convert vertical feet to meters. Also, overlaying the UTM grid (1km by 1km) on a map allows for relatively precise determination of distance, without the aid of digital technology. A good first approximation for the time necessary for an alpine unit is 15 minutes or 4 units per hour. Although individuals may be much much faster, the time taken for a unit must be constantly observed and used for planning forward progress both in the short and long terms. Note, an old and wise mountain guide says that this equation needs modification when the terrain is very flat (<5°) or very steep (>35°). When it is flat, only consider the distance, when it is steep, only consider the height.
The number of alpine units sustained per day over the course of a week is an important result of reflection when planning the next ski traverse. A first approximation of this sustained progress could be half of the normal alpine units done on a day's ski tour. If you are strong with a heavy pack, take 3/4 of the speed on a day's ski tour.
Alpine style ski traverses allow for continuous replanning of the route, fast exits, avoidance or mitigation of bad weather, and, my favorite, complete immersion in a mountain range. This is the approach of the pioneers of ski traverses, light and therefore fast and nimble. Bill Briggs did not have a sled on the Bugaboo to Rogers Traverse. With the constantly improving lightweight gear, improving map material, denser weather observation networks, improved remote sensing data availability and access, this practice can become safer and more enjoyable with time, especially when experience allows you to whittle down your kit, and you condition yourself further.
In my case, my pack can weigh a maximum of about 25kg, including skis, and I am still having fun. I aim for 40 units per day, which assumes some poor conditions and some good conditions for progress. My daily progress on my last traverse in Bulgaria averaged at about alpine 45 units per day sustained over 8 days, including a rest day. That's not fast, but it suffices to cover considerable ground (360 alpine units total). I used 106mm wide skis and freeride bindings. I could have been faster with narrower skis, lighter bindings, or scale-based skis. I have much room to learn and improve.
I am thankful for the concise book on winter mountaineering 'Bergsport Winter' in German. I am most thankful for all my mentor's and friend's guidance and patience. They were pivotal in aiding me to develop the necessary skills of determining avalanche risk, orienteering in all conditions, detailed map study and route planning, as well as little bits of information to make prolonged stays in the often harsh winter landscape enjoyable. They continue to be very helpful and good company. Thank you!