Need moar fans

I'm using a Phantom 410, and whilst the temps are good, I can hear the fans even at 5v... call me picky.

Anyway I'm a silence freak and looking to replace the fans with silent ones. Looking at reviews it seems the Silverstone SST-AP122 a steal/too good to be true since they're only 5 quid.

I'm planning on running two 120mm's in the front as intake (unless 1x 140 would be better?) and two 140mm's in the roof, the exhaust is taken by a radiator, side and floor panels taken by sound proofing foam.

I'm not really sure what I should get for exhaust fans?

Sorry for the long post, help is appreciated.

Thanks.