This to me looks like a good gravel tire. I think I might give these a try in the 27" size (I don't see anything else like this that comes in 27"). I don't know how flat prone they would be, but I think they would look great and function well for a gravel grinder, especially for the price. The reviews say the tire is a little narrower than advertised but I like that.
http://www.cyclocross.com/product/ke...Feg-MgodOVkAWA