Even if the 90mm does move more air, it does so over a smaller surface area. So I think it won't work as well as a 120mm which covers the entire surface area thus better cooling.
If you were to put a 120mm fan that moves more air on it THEN it will cool better. This is the fan I put as my intake fan & it moves a TON of air!!!
Scythe SY1225SL12SH 120mm Slipstream Case Fan.
Air flow=110.31 CFM