Ha - @umop3pisdn has beaten you to it there!
I always found the aksiums very 'soggy'. The Zipps aren't that much lighter, but feel a lot more responsive, stiff and reassuringly wide. The smaller, better tyres help aswell, I don't think that 30mm Strada Bianca are a good choice for a predominantly road orientated bike - I felt like I could never get them up to pressure, that they were always spongy under duress and compounded the unresponsiveness and general lack of stiffness in the wheels.
Don't get me wrong - they were both super super comfy, just found a noticeable difference keeping up on club runs.
Do need to do something about the bloody branding though - anyone got experience with removing these off a 30 Course wheelset? They're printed on, not decals :(