the allez sprint lets you basically switch the shifter cables so that there's less cable housing bend in the front, because the BB portion easily lets you cross the cables back to their correct ports. however, has anyone actually seen wind tunnel data that tests the allez sprint? specialized say it's just as aero as their old venge (of course they would say something like that). where's the data? i can see the attraction though. it's a good looking frame. I'm just skeptical that all these bike manufacturers all claim their product is the best. it's BS
I don't believe my caad9 frame limited me in any way. After I totaled my bike, I went on craigslist and got a felt 3c frame, which was relatively cheap, and it does the job well enough. the next race bike will likely have disc brakes on it.
I never was able to test an aero bike vs a non-aero bike, all other things constant. it's very difficult.. the most important thing is probably the geometry and fit. you'd get a bigger aero gain going from 44 cm bars to 40 or 38, than spending $1.5k on a pair of zipps. that's the sad thing I see people do. They roll around in wheels that cost more than all my bikes combined, and they're wearing non aero helmets, with upright bike fits.