this is like the questions about steel and aluminum as frame materials.

the design has more to do with the material, or in this case, the size.

OS is stiffer and stronger if you make it to the same design specs and just upsize it, obvoiusly, because of the greater mass and area subjected to (presumably) the same stresses. however, it's also less aerodynamic.

for all intents and purposes, YOU won't notice a single difference... mostly because they design each to its own needs. TT bikes usually use a 1" hs to cut through the air... but until you're cat one i don't think you really need to worry about it. just get what you want, make sure everything fits, and if you need spacers use the right ones.