yeah, that's the thing, most of the time you won't be in a ground blizzard, but if you decide to go backpacking in the sierras or the rockies from november to march there is definately a chance of that happening so you better be prepared or pick a warmer season for your trip.
the tarp needs to have full closure on the ends. i think the sock would take care of anything drifting in from under the edges or through the suspension opening. insulation is less of an issue as the low tempreture part has been dealt with sucessfully by quite a few. that leaves only the wind. so all that remains is what does a tarp that can confidently handle 50+ mph wind gusts look like?
jeff, i'm guessing you didn't have a wind guage at winnemucca so you wouldn't know how hard it was blowing. i've heard 70mph is when it gets very difficult to walk or stand.