tarps can be used for wintercamping, especially below the treeline, they are actually very handy in deep snow conditions where you can dig out a cozy space and block the sides of the tarp with snow and also if you have the time, pile up the back and half the entrance. I think Silnylon would be a good choice, any lighter may rip with snow loading, any heavier and, well more ounces.
I do my winter camping in mid shaped tarps. My favorite is the megalite black diamond, but i havent used the Hex shaped golite or Oware mids. The golite looks like it could possibly get a quicker pitch, but you'd have to ask someone else. I prefer no flaps, and digging in than having spindrift flaps.