Just ordered a pair of these to replace the top rad fans. I noticed today that they weren't pushing much air through the radiator and ontop of that, a lot of air was being forced back through the fan instead so hopefully these will do the trick
http://www.overclockers.co.uk/showproduct.php?prodid=FG-008-CS&groupid=701&catid=2331&subcat=4
http://www.overclockers.co.uk/showproduct.php?prodid=FG-008-CS&groupid=701&catid=2331&subcat=4