Aelle and Gara are the only two Columbus tubesets I'm aware of that would use that size of post and they're only 45g difference, which is due to the heavier gauge Gara seat stays. Given that the density of the various steel alloys do not vary by a considerable amount, one possibility is that one of the frames is tretubi Aelle and the other factor is the selection of fittings. You'd be surprised as how much weight difference the latter can make, which is why I never use frame weight as a tubeset identifier.