Which 60mm CPU fan in G4 Quicksilver?



I'm wishing to change the 60mm CPU fan in my G4 Quicksilver tower.
I know that many sites refer to quieting their Quicksilvers - however I'm finding it very hard to obtain a fan (or information regarding brand/model) that has adequate CFM but is also quiet.

The original fan is as follows:
> Sunon (green label)
60mm x 60mm x 25mm
(magnetic levitation system)

I'm finding it very hard to believe that this fan is pushing 23.5CFM of air as it really does not seem that strong at all. In fact it is the lack of CFM of this particular fan (rather than noise) that is forcing me to consider replacing it. I have a 867mhz G4 that I will shortly be overclocking to 933mhz - and the heatsink gets quite warm already. I have a fan controller - so a higher specified fan is okay. I have tried a few generic PC heatsink 60mm x 15mm fans, and although they increase the airflow - most were accompanied with unnecessary noise. Furthermore, I have increased the size of the holes where the air enters the case below the telephone jack. Given that the current (apparently) 23.5CFM isn't cutting the grade - I'm looking for something slighly higher. But, of course, without too much of a noise hit.

Someone suggested this fan to me:
Delta AFB0612EH
(- using the fan controller I could turn it down)
> However this is the very fan that caused all that trouble with the G4 MDD PSU noise - so I'm dubious. Also, I'm aware that Delta fans in general have a whinning sound.

If anyone has any suggestions.....