not sure of actual CFM but the fan stops increasing in speed at approx 4000rpm as this is the max rated speed, and the clutch does it job from there on.
I have fitted my clutch fan back in, and because of the cooler pip[e i had to trim down the blades, Used a large file on the edges with the motor running, then the pipe did the rest, theres acctually quite a fair bit trimmed off the outer edge now... Im guessing as a result im going to be sacrificing some of the maximum rated airflow...Ive kept the thermo fan on the front of the rad... just in case i spose.