The usual heat sink calculation uses just surface area and linear air flow.
If you really crank up the air flow, maybe pin fins are better, because maybe the extra turbulence increases the temperature gradient near the fins and so makes the heat transfer better. However, the heat capacity of air is pretty small, so I sort of expect that the temperature gradient might not get that much sharper. For a given back pressure (which is all you get from a muffin fan), I sort of doubt pin fins are an improvement.
I don't have a slam-dunk first principles calculation of that, though, which is why I was wondering about data.
Cheers
Phil Hobbs