When Jon Seifert was conducting his research into ski width we were communicating on a regular basis, this is the summary that he sent to me, prior to the study being released:
1. Wide skis resulted in a large range of acceleration in the vertical and longitudinal planes. This would indicate more skidding and vibration with those skis
2. Wide skis had lower relative forces than the narrow skis due to significantly more skidding and that skiers turned closer to the fall line (more parallel). The skiers arced their turns much more with the narrow skis.
3. Skiers skied more two-footed on the narrow skis than on the wide skis.
4. Edge changes were faster with the wide skis. This would indicate less arcing and straighter turns.
5. In free skiing in the steep runs, edge angles were significantly less with the wide skis. This would indicate that it’s more difficult to get the ski on edge due to a longer lever arm (distance from binding edge to the edge of the ski).
6. Wide skis result in greater external rotation of the thigh. This may be due to greater overall rotation of the body.
7. The wide skis force the knee to move more transversally (medial and lateral or inside and outside). This movement along with the rotation creates more torque at the knee.
For those who say edge to edge is faster on a narrower ski, see point 4. What you are focusing on is the theoretical lever arm, and not how the body interacts with a ski. On a wide ski, on 2D snow (and very few here are heli / cat guides) your turn tends to come from the upper body. Show me someone who regularly skis on 90 + in 2D snow. Video them, and I'll show you someone who initiates with their upper body.
When you do not ski from your feet you execute big, inefficient movements. You jam from outside ski to outside ski. The consequence of that is that the ski never loads properly, which is why when we design a wider ski, we design it softer (for that reason and others).
On a narrower ski you have a better opportunity of skiing from your feet - i.e, more efficient. You finish one turn. You go into transition. You are in a place of neutrality - equal weight on both skis. No edging. Every efficient turn executed by a technically proficient skier has this phase - even if you do not see it without slo-mo video.
When you come out of the point of neutrality part of the process is to progressively weight and pressure that outside ski - just enough so that you bend it. That progression gives you the best opportunity for control throughout the greatest percentage of your turn.
That process above is why I tend towards a narrower skis. My everyday Western ski is 79 underfoot. I recently purchased a pair of Head Kore 99s. They are a hoot in 3D snow. However I have only skied them maybe 25% of my days since we started seeing 20' - 80" weeks.
Want more? Look up Jon Seifert's studies. Clinic with Robin Barnes.
Enjoy.