The difference between you+bike with 420's and you+bike with 404's is like point two percent.

in hard acceleration efforts, zipps can feel sluggish due to extra wind-up allowed by their rear hub lacing pattern. their trade-off is greater lateral stiffness, but a lot of people say they feel less snappy.
some wheel test somewhere (possibly rouesartisanales, but maybe tour mag) showed approx double torsional flex over competitors. note that this affects "feel", not necessarily performance

In other words, it could be the most sluggish feeling, flexible wheels, and on a flatish course, most aero would still win. Hell you could probably run 2200 gram wheels and as long as they are aero, you'd still be faster.

If you want to be aero, tape over your helmet vents. I'm sure the weather at this time of year shouldn't be too much of a problem...

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Slam your stem.