Just boxed up Corsair CX750M's and pulled the stock fans out of the S5's. Replaced those with Corsair SP120 fans. Replaced PSU's with an evga 1300G2 Supernova.
Right now window cracked open - running cold air intake mode! Once I figure how they will rest will secure them then get on that red cable management. What a mess.
Couldn't be happier with the new fans or the new power. Love these machines, especially now that they are liveable and silent compared to stock.

I ran the SP120 High performance on my S5's and they couldn't cut it. Ambient temps were about 65F and the temps went straight to 65 or higher. Soon as the warm weather sneaks in, those fans will not be able to cool it sufficiently. I opted for the Noctua NF-F12 3000. Used two of them on each S5 and brought the temp back down 10 degrees. A lot less noise than stock fan, but not silent either. In between, but dooable in situation.
Good luck!