For more Power Supply info, go here:
http://forum.sslmixed.com/index.php?topic=580.0My 1991 G-Series Supply has the 4500N
http://mouser.com/Search/ProductDetail.aspx?qs=DB9cKZ5ZWfX%2fCr5Go4OHYg%3d%3dTwice the airflow + twice as loud.
At one point SSL stopped putting in a third fan (next to the regulators), but maybe thats when they switched to the stronger (2) fans.
I actually think it could be even stronger, and I have also recently recapped my regulator cards, and they are definitely suffering from the heat as well, so... I don't know about leaving the 3rd one out! You want your supplies to be cool, that should be the priority!
Also, ebm-papst has a newer model with similar specs out that is 10dB quieter, has a higher airflow, and only a third of the old model's power consumption. At mouser.com, it's tagged "new technology".
ebm-papst ACi4410HH
http://de.mouser.com/Search/ProductDetail.aspx?qs=%2ftUMGyzD9cIlsfLdcf3cPQ%3d%3dI'd go for two or three of those.