Hi Monte-
I've found that wind speed needs to be about the same as on water to snowkite, however, the snow conditions & terrain are what dictates the kite size... at least it is for me. The deeper the snow the bigger the kite. I've sized up to a 11m in conditions I would only kite water with a 7m or smaller. The snow was knee+ deep and on the heavy (wetter) side will some hills, so the only way to get moving in that deep of snow and with the slope angle was to size up. On the other end of the spectrum, I've sized down to a 7m in wind conditions that I would need to fly a 10m or larger if I was on water because the snow was so firm.
Snowkiting on terrain and hills is much like riding in the surf, so having a slightly bigger kite will help you get over tough sections or up a hill a lot easier.
I understand the principals of altitude and it's effect on the air density causing some to size up in kite size in order to get enough power, but I find this concept only holds true on water because snow conditions and the given terrain will always be the determining factor of what kite size to fly no matter how high up you're kiting. Example: I've kited almost identical conditions, terrain and winds at two difference spots with nearly a 4K foot variance and a 20+ degree temp variance and I still used the same size kite. The conditions dictated the size I was on, not the altitude.
As for me... I'm still waiting for the coverage to get a little better in the Sierras. Stay tuned!
