I think we should all read the fine work done by Jan Heine of Vintage Bicycle Quarterly (now renamed, Bicycle Quarterly). After numerous tests he found when constructed well, some very large tires, such as a 37 mm Mitsubishi 650B, rolled as fast as quality 23C tires. I was stunned. Further, some tires that came in 20, 23, and 25 mm options showed the 25mm option to have less rolling resistance. Also, it was found that higher pressure didn't mean less rolling resistance. If you can obtain a copy it will challenge several long held beliefs. Tire choice was the most critical thing to purchase for riding faster on long rides such as PBP. I would forward the article but it does not appear to be available from their web site at http://www.vintagebicyclepress.com/vbqindex.html