If an "i" model is bought then link gives you control to build your own curves, which can also have profiles for things like night and day gaming.
So they can run over night and such being a little quieter a letting the temps rise a little bit, but with ambient temps lower normally there is not so much noise change.
You should find that the standard SP120L fans will run from around 800-2700RPM so you can go from silent to hideously overkill when needed. The fan speed is controlled by Corsair Link within your OS if you go for the H80i/H100i, there are 3 default curves, custom curve, fixed RPM, fixed % and maximum speed to choose from. You can also control the light on the pump unit to any colour or brightness desirable and make that vary with temperature. Once your happy with all of your parameters you can save them to a profile and then load different profiles from the software or an icon in your notification tray.
I have SP120 PWM editions which are the ones to go for if you intend to control them with Corsair Link although apart from aesthetics, vibration damping and possibly slightly lower RPM at the bottom end they bring no performance gains over the stock H80i fans as they have the same blades. In short if you don't care how they look stick with the stock fans, if you want to keep the flexibility of the original fans go for SP120 PWM's and if you just want to run stock all day at a fixed RPM go for the SP120 QE's.
Just for reference here is a screenshot of mine. (ignore the extra lights and fans)