I had ventilated seats on my Mercedes ML, Nissan 370z Roadster, Jaguar XKR, Range Rover and now on my X6m.
I can make a comparison...
1. The purpose of the ventilation is NOT to get you cool, but to not sweat and have a wet shirt.
2. if you feel an Icy breeze, go a level lower, as this is not good for your lombar area.
3. It depends on the temperature of the car.
If you let 10min the engine + seat ventilation running, you will see that the seat is cool.
That is because the air ca flow when you are not on the seat, obstructing the way.
On the Z, the ventilation was used like a blower for heat or cool and it was brutal, but it was a convertible and the temperature with the top off can be extreme.
See the system
here.
On the usual cars, the seat fans are not powerful.
RR and Jag are the faintest systems, ML & X6 are medium, and Nissan 370z Roadster was the extremist...
BTW black leather, no ventilation and sunny days = hell!