Up here, a foot to 15 inches is actually ideal; anything over that in one dose gets to be a pain in the ass. Newbies cant handle it all up here when it gets like this. I have been in your type of dry continental snow chest deep and can still maintain speed on relatively gentle slopes. If someone can ride off piste in the PNW, they can ride anywhere.
im going to say that anything over a foot to 15" anywhere newbies cant handle. one fall and getting buried and a rider unfamiliar with deep off piste pow could lose their shit and freak out trying to escape, not to mention being unsure how to get going again or find their way out. the only down side to having a shit ton of pow (2ft range) is that you are limited to what you can ride due to how steep of a slope you have to be on to make it down.