How quiet do you want?
As quiet as possible?
The one I have now is fine, but theres definitely a noticeable white noise of the fan and its by far the loudest component (though thats relative to the near silence of the CPU and exhaust fan).
As for the requirements, below are the specs of this machine. I used the Outervision PSU calculator which estimated around 300W, so I just rounded up to 400-450W, but perhaps this isnt necessary?
Video:nVidea Gefore 210
MB:GIGABYTE GA-78LMT-S2P AM3+ AMD 760G Micro ATX
CPU:AMD Phenom II X6 1045T 2.70GHz AM3
Memory:Kingston Technology HyperX 8 GB (2x4 GB Modules) 1600 MHz DD
Drives: (1) 2TB WD, (1) OCZ Vertex 4 512MB SSD, (2) Samsung 256MB SSD
And as mentioned in the OP, it cant be more than 140mm in length to fit the Silverstone ML03 case.
Thanks again guys.