Why are you limiting the choices to 27" wheels? I ask because many bikes built for 27" wheels can handle 700c wheels with only slight adjustments of the brakes, the availability of tires in the 700c sizes is better, and the cost of a new 27" wheel is probably very close to that of a 700c wheel. Is there an unusual technical challenge you're trying to overcome, like very particular cantilever brakes on a touring bike?