I've got multiple sets of Zipps. Old 404's, 303's with the torroidal, dimpled, rim, 808's with the torroidal rim, and now 404 FC clinchers.
I can't say I can tell any speed difference between the new and old 404's. Of course, any difference would be small enough as to not be perceptable.
As for handling in cross winds, the new design might be a little less prone to getting moved around. However, I haven't ridden them enough in stiff winds to convince myself that's true, or to rule out the placebo effect.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.