I'm on 700x32 Marathon Plus tires. They feel pretty slow, but I'm pretty confident about their flat protection. That said, I won't be buying them again, but I'm not as disappointed with them as some people seem to be. I knew they'd be slow when I bought them and they are. I heard they'd hold up well against flats and they have. But for my next tires I'll definitely try something lighter, probably Vittoria Randonneurs.