There is no one answer to your questions, Jons. Drag between an ICF K1 and a ski like the V10 is different. In the K1, skin friction resistance is low but wave resistance is high once you get going pretty fast, i.e. 14 kph. A strong paddler can "overcome" some of that wave resistance in a sprint, but at marathon pace, you're left with the sum of regular friction resistance and wave resistance - most of which is wave resistance in the K1.
On a ski, the wave resistance is less, but friction resistance is more than with the K1. One therefore does not hit that "wall" of wave resistance that is encountered in the K1. But, then, you can't push over that "wall" with the longer ski in a sprint, either.
At lower speeds, when wave resistance is low, the K1 should be the more efficient boat for energy/distance calculations, generally speaking. At higher marathon racing speeds, the edge should go to a boat with a longer waterline - something like the V12 because its wave drag is so much less than the K1's wave drag, even though it has higher skin friction drag.
Also, a speed comparison between an ICF K1 and a ski depends on the weight of the paddler. A lightweight paddler will be faster in marathon and sprint in the ICF K1, but a real heavyweight paddler (like Oscar) will be faster in a marathon in a ski like the V12 because the K1 is too short and too narrow and sinks too low in the water to be an efficient hullform. For a sprint? I don't know, but I think the heavyweight might be faster in the ICF K1 if he/she is powerful enough.
From what I understand, the ICF K1's speed is limited by its short length - even though it's still an incredibly fast boat. I've read that the optimal K1 length for an average weight male is somewhere around 6.5 m. I believe it's like rowing shells in that there is a different length and width shell that is optimal for a paddler of a given weight.
Even though they make K1's for "heavyweights", they're tweaked for a better wave profile while keeping within ICF overall length rules. They also have bigger volume decks to fit the bigger paddlers. And conversely, the 21 ft skis aren't the most efficient hullforms for the 55 kg paddlers on flatwater, either.
Erik