[...] noticed no difference between flat based, slight edge pressure or carving. In each case, the glide was the same as far as I could measure.
My testing suggests (hiking GPS that gives highly accurate speed data), that edge pressure generally doesn't make a difference (as long as the board is still going straight). In cold, fresh, non-icy stuff and wet snow it's even helpful to use a significant amount of pressure, so that only part of the running surface makes full contact.
When carving, even if you have the same glide/speed, you are not going straight and have to cover a longer distance. So if the goal is to make a flat/uphill section, it's counter-productive.