If they were the same size, but in my Veloflex the clincher 25 measures smaller than the Tubular 25 of the same case. I had Vittoria too and did not measure. But while both road well (I road the Vittoria clincher on my front with a latex tube) the profile looked about the same as the 23 tubular. Vittoria uses the exact same made-in-Thailand stamped tread on both, and FMB did buy and use that tread (and I expect others).

But to my picture posted of the 1720g set http://www.bikeforums.net/19154969-post37.html- show me that for 2300g in a clincher. The whole system is heavier. The rims are heavier, add rim strip, tires and tubes and getting the equivalent air under there is going to cost about 600g/pair. Then in many cases you just don't have the same options in clinchers. I think the value best tire for this application is the Veloflex Vlaanderen which measures close 28mm but is not available in clincher. That the OP rider does not want to use tubulars is fine with me. I will ride clinchers this morning. Just that all nonsensical arguments aside - you cannot get the net result from a clincher wheelset you can from a tubular wheelset. I have posted mine. I have both.
Here is the 27 (measures 28 and is taller than expected) Veloflex Vlaanderen:
TarmacClearance.jpg