When we were in the UK, we used gatorskin year round on the tandem. No real problems, except when they start to wear they can suddenly become very prone to flats from flints. We did have comments from people following us who were surprised by the amount the rear wheel would drift though. While in California we've switched to using GP4000s in summer, 4 seasons during the rainy season (yes, it rains and rains *hard*). If you are happy with the gatorskins I'd stick with them, there's no need to proactively change them.