All of the Strike-X Power supplies feature a very quiet 139mm fan with noise levels starting from just 16 dBA. The noise level will increase depending how much wattage the PSU uses to power the system (take a look at the graphs at the bottom of this page for more information). 

The PSUs are physically the same size with the major difference being the wattage they provide. Also the 800 and 1100W version are modular unlike the 500 and 600W PSUs. The only other difference worth mentioning is that while the PSUs are 80+ certified, the 1100W model is 80+ Gold which means, at its peak, it is over 90% efficient!