I think you're missing the point of winter wheels: you need more tyre wall height to cope with winter pot-holes, etc. Plus higher profile tyres are cheaper!
17's are on the limit and 18's are pointless for winter wheels unless it's just a sacrificial set of wheels that you don't mind cracking to pieces, etc - but given your other wheels are reps, I'm not sure why you don't just buy another set of those.
17's are on the limit and 18's are pointless for winter wheels unless it's just a sacrificial set of wheels that you don't mind cracking to pieces, etc - but given your other wheels are reps, I'm not sure why you don't just buy another set of those.