Either swap out the fan in the XFX or get a new psu with a quiet fan.
There are a number of psu's where the fan doesn't spin up untill 40-50% load.
As to fanless psu's 550w is the biggest (that's the one I own)
but it's doesn't have the amps to run extreme gaming cards (mine's a GTX460 @ 850/1700)
Converting a fanless psu to be watercooled is possable (blocks stay on the outside of the psu case)
but the koolance psu is only slightly more and you get a warrenty.
Fan swap out or new 'smart' fan cooled psu is a better option