IRC Roadlite Tubeless 25C = 26.8mm
Continental GP4000S 23C (latex tube) = 24.7mm
Schwalbe IM Tubeless 22C = 23mm
IRC Formula Pro Light Tubeless 23C = 24.6mm
Hutchinson Galactik Tubeless 23C = 22.5mm
Hutchinson Atom Tubeless 23C = 21.8mm
As you can see, the IRC Roadlite Tubeless 25C measures nearly 27mm across when mounted on the Zipp rim...that's HUGE. It makes for a great road/training tire, especially on the rear, and in fact that's what I've been using for that purpose for the last few months. For front tire usage, especially due to it's narrower width and aerodynamic features, the Schwalbe appears to be the best of the bunch. The Hutchinson tires are narrow, but their Crr values are not so great...plus, it was my experience that the Hutchinson tires were significantly more difficult to mount (tight beads) than the Schwalbe or IRC tires. As for the IRC Formula Pro Light...that one is a bit of an enigma for me. It's Crr is in the "decent" range (not great, but not horrible either) but it seems to be the most fragile of the bunch. I used it for a short time as a rear tire and quickly suffered punctures large enough to not allow the sealant to work...and I think there are better choices for front tires...so, I'm not sure where I would actually prefer using that tire. That's a bit disappointing really, because I think that it's unique latex based air barrier layer is the way to go for tubeless applications.
After having ridden and played around with road tubeless offerings over the last few months, I've come to the conclusion that the purported "advantages" of running tubeless tires (with sealant) in road applications are really only realized if the vast majority of your punctures are from relative small items (i.e. 1mm or less). Anything larger than that, and the air volume is too small and the pressures too large, for the sealant to effectively seal AND let you continue riding...with cuts or punctures larger than 1mm, you will most likely end up having to pull over and swap in a tube anyway. So, if most of your problems with flatting are due to things like goatheads or "michelin wires", then tubeless with sealant is a really good way to go. If you instead have problems with things like "pinch flats" (from hitting sharp edges or objects) you can actually get a significant improvement in performance just from using latex tubes and/or larger width tires. Sure, latex tubes take some unique setup considerations for reliable use, but they're really no more of a hassle than setting up a tubeless tire using sealant...and in some ways they're easier on a day to day basis.
Vittoria and Specialized Results
Over the past few months, I've been testing some tires for Greg Kopecky and Slowtwitch.com for inclusion in some review articles he's written. An example is seen here (http://www.slowtwitch.com/Products/Things_that_Roll/Tires/Specialized_Road_Tires_2014_3982.html). Listed below are some additional tire results that I'm adding to the overall Crr spreadsheet linked to in the upper right of the blog.