Ok so I've drawn some pretty lines around the rim profiles of the A23 (left), HED C2 (middle) and Bikehubstore C472 (right).
Based on a decade or so of professional experience, this is how I presume to the flow to behave over all three rims. The curvature of the trailing edge of the A23 is so sudden that the boundary layer will separate at point 'X
'. This of course would create a large wake.
For the HED C2, the initial curvature is smaller, however it then quickly begins to taper so the bounday layer would most likely separate slightly further downstream. A smaller wake would be created.
The C472 is a longer rim and its trailing-edge curvature is even smaller. Hence the boundary layer would most likely remain attached almost until the trailing edge. This rim profile would be the most aerodynamic.
If you look at the profile of the Corima Winimum it resembles a shorter version of the C472, rather than the Hed C2. By that I mean the actually trailing edge is thicker, however the curvature that leads towards the trailing edge is more gentle than on a HED C2. The actual thickness of the trailing edge doesn't make much difference when dealing with such a short aerofoil section (treading rim depth as aerofoil chord). It's the curvature leading up to the trailing edge that is the crucial design parameter that will determine boundary-layer separation.
Of course, these diagrams assume the 'worst-case' position of the rim in the 'tyre-leading position' where the rim is at right-angles to the flow. As you move towards the top/bottom of the rim the effective chord length grows.
When dealing with 'rim-leading' position, there are other good reasons why a thicker and rounder trailing edge is better, primarily for slight angles of yaw.
One day I might throw these profiles into a CFD package (e.g. FLUENT, Open Foam) and see what sort of numbers pop out. You'd have to make some assumptions about tyre size/shape though, my tyres in the pretty picture above don't seem to have enough sidewall.
I think I might buy a pair of C472 for my next wheel. Same weight as the HED C2, slightly better aerodynamics and about half the cost. Who makes them? Kinlin?