use tools like this:

http://aeroweenie.com/calc.html


If there is not much wind there will be essentially zero difference between the 40 and 60mm deep wheels.

If there is some wind, then you are looking at at something around a minute difference max.

I'm not sure how the aero of the carbone (there are many varieties) compares to the FFWD wheels, but the weight difference would only add a handful of seconds

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Kat Hunter reports on the San Dimas Stage Race from inside the GC winning team
Aeroweenie.com -Compendium of Aero Data and Knowledge
Freelance sports & outdoors writer Kathryn Hunter

thanks, that is what I was looking for

So even the most cutting edge aero finishes now are a negligible improvement on older technology? and the 40-60 thing's a wash I suspect meaning the 30 percent price difference is for about a minute. the entry for a minute - pretty sure that i'll lose more than that in the swim

Well as far as I know the FFWD rim shapes are far from cutting edge aero technology. It's still a narrow rim right? So not the newer toroidal shape, more of a bulbous V shape like most Chinese clinchers.