I run them and think you might as well get any marginal gains. You need pedals, my preferred pedal is Speedplay so may as well get the most aero set. As for the stack adaptor for any marginal gains they give, I'm not into sending my shoes away to the UK plus cost involved and having holes drilled in them to accommodate. I like to be able to sell my old shoes.

 
http://www.ero-sports.com/...lay-zero-aero-pedals

http://speedplay.com/...=home.slipperypedals

Bottom line is that they do provide significant gains (even without the one-sided aero pedal). They are both lower profile than Look/Shimano, and you can add the aero cleat covers easily.

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I keep being pointed to this page as proof that speedplays are faster than others, yet I always find this:

"Now, what we didn’t do was test the Speedplays against other pedal systems (i.e. Shimano or Look) because it’s difficult and time consuming to accomplish."

I think gains are lower than the margin of error of measuring equipment in a standard windtunnel setup so that makes sense.
They are just very nice pedals (low stack, easily adjusted etc...) so enough selling points.
Sam

It's worth noting the two sentences after, though.

Sure, but no data. The bottom line is there is no available objective data to choose speedplays over other pedal systems for aeroness.

This is my takeaway for now as well. They are more aero than standard speedplays (probably), but unknown against Look/Shimano. I'll still use my Vectors unless their is more substantiated evidence that they're costing me 5w+

They seem to have ditched the aero model. Not sure why as it seemed pretty popular in the TT scene here.

still on the website, so why do you say they ditched them?

Well there's objective anecdotal evidence (Jim@ERO tell us the data exists, and he's seen it). Objective in the sense that Jim doesn't sell Speedplay, afaik, and has no particular self-interest in promoting it.

Combined with eyeball windtunnel - the Speedplay with aero cleat is low stack and clearly shaped in something that looks pretty aero.

Combine that with it being a good pedal system just as a pedal, and it's enough for me.

Unknown data as the number is not disclosed. But don't forget he says the comparison is very difficult to do. I.e. choose the pedal you like best, forget the aero numbers

More data: https://quintanarootri.com/...h-performance-center

Matt Hanson saw a 4W improvement and spent his own money on Speedplays after windtunnel testing - he appears to have been on Time Espresso pedals before.