The Spal 11" runs at 37mph in static air.
Impeding air is not a concern for these systems.
If cars only operated at cruise speeds in reasonable ambient air, no one would need a fanned unit at all, but that's not the case.
The other part of the equation that's being left out is recovery time. Even if a car is operating at cruise, after it's shut off it's sitting there baking. Key on/pump on and it'll move fluid, but until you're moving at cruise (or at least 35+mph) again, you're not getting anything over the core regardless of it's size.
Our triple pass/dual fan unit is superior to the one I have on my 07 Gt500, but it (a dual pass/dual fan with 10" Spals) will drop IAT2 from 170 at start up to 120-125 in less than 90 seconds while sitting still. This is after a pass and a 45 minute rest in the pits with no fans/pumps running.
Just some data and food for thought.
bj