Analysis of video showed my foot tended to roll. Standing on bare feet showed my left arch tends to collapse. Vargus adjustment on L foot from Specialized shoe was required, with stabilization of foot using firmer pedal. I was told that Speedplays can get sloppy as they wear, and cleat can get sloppy as adapter plate or shoe surface wears, and in any case free float of X-series can allow for sloppy habits. He thinks Zeros can be made to work if in top condition and if float is minimized.
I think this is topical because these pedals have very little rotational float, so that this may be an asset as opposed to a detriment is a consideration.
Sorry, not to go off topic, but on this same note, over the past 18 months, I've notice my speedplays, even with the screws on the bottom set for no float, there is the ability to rotate/float some. I've got no rocking left/right, just the loose float...doesn't bother me and never had any issues.
My concern with these is accidental ejection. Seems if you foot moves inward/twists while some kind of lifting is going on somewhat, your foot could come out? Don't know, really would have to try some...but that price is steep. Easier to just buy a new set of Speedplay to deal with wear and tear at 1/2 the price every few years.