3 fans... Seems a bit overpowered? Is it possible to turn off fans...?
No, but they will stay quiet as long as the card is cool and only adjust to keep the temps down.
AC makes some GREAT coolers.
EDIT, also check to ensure your current board is a reference design. look at the back to ensure it is similar to this. You want everything to line up.
make sure the hold line up and all that good stuff.http://www.ixbt.com/video3/images/ref/hd5850-scan-back.jpg