I just bought my third set of Marathon Supremes in size 700x32 last week. There is something different about the new Supremes. My old set did run narrow, but the new ones do not.

The new tires caliper out to 31.8mm wide at 75psi on Mavic A319 rims (the tire is rated for 55-95psi). Surprising, the tires only weigh 325gm each! I weighed both several times with my digital scale to be sure. I even weighed the old set and the tires were 370gm and 380gm. Whether that means there's less material in the casing now, I don't know. The new tires ride as well as the old ones did when they were new. Too few miles though to know how long they'll last. I got about 6000 miles on the first set with one flat over its lifetime (tires were bought in 2009). Actually, the tread on the old front tire is still okay and will be used as a spare. The second set that I bought in 2010 has about 5000 miles on it and is still in use on one of my bikes. Never had a flat with the second set.