I have about 2,500km on a set of schwable carbide studs.. mostly pavement, they're going to last about 7,500km before the central studs are worn out which leaves the outside studs mostly unworn which are the important ones to catch you from sliding out... so the tire will still have life left in it after that.

Also consider you're sparing the other set of tires from that use... so the summer set should last you a lot longer.