hmm, normally the fans that come with the heatsink have more RPM's than normal, but at the same time these fans does come with smaller size.
as if your heatsink already has 80mm fan, then from BIOS, check ur fan RPM, as if they match or even below the rpm's of the fan u r trying to install, then NIKE (means Just Do it!)
Intel Core2Quad 2.66Ghz 12MB L2-Cache
4096MB DDR Kingston Hyper-X
XFX 9600GT AlphaDog
Seagate 2 X 320GB SATA2
LG L246WH Flatron 24"