You should have about another 1/2" to 3/4" clearance on the 54 compared to 56. The top tube on the Allez is curved-- You don't need to standover the mid section, just the part 3-4" in front of the nose of the seat. You're looking for at least 1" standover while wearing cycling shoes (if not clipless, whatever you will ride in). Some people say you need 2", but I clear my TT by less than 1.5" and I've never smacked my junk.