you could put more organic feel to the choir, OR you could go even more synthetic and give it those sharp cutoffs and attacks of the Super Metroid days, if your samples hold up that is. When I think of wintery choirs, I imagine very sharp attacks with little to no marcato.
Well, obviously your track got my ears turning, so suffice to say tha I quite like your track, it's wintery without being Christmasy and dramatic without being melodramatic. Nice!