Most Coolermaster 120mm fans have very low CFM and with a dust filter it will be even less.
Honestly I didn't notice any difference in temps on my GPU with 2 side fans for intake.Maybe 1c at most.The biggest thing though is of course cooling the GPU itself but also to cool everything else on the PCB.I'm sure having fans pointed at the card will increase airflow around the VRM's and RAM chips.