I have the Silencer 610EPS12V (2 actually), as well as a few Seasonic S12 II's.
They are, contrary to what continuum says*, in the same class acoustically once they're installed in a system.
The Seasonic is quieter, but not significantly so. A whisper vs a somewhat louder whisper.
The PC P&C is very close in noise output to the Seasonic unless you manage to get the Silencer near full load, which most systems will never do.
That said, you won't come close to putting either unit under any kind of strain with the system you've spec'ed out. You could go as low as the Seasonic S12 II 330W, but the 380W version is probably the best balance for most systems out there.
Unfortunately, PC P&C currently don't offer anything I'd recommend (except for specific needs) below the 610, but hopefully that will change with time, as I also prefer the large single 12V rail.
Regarding the HD choice, as continuum mentioned, you should take a good look at the performance numbers for the newer 500GB - 1TB drives next to the Raptors. The Raptors are an overpriced, undersized drive when you realize their one remaining advantage over modern 7200RPM drives is mainly in their lower access times, which really doesn't make much difference outside benchmarks these days.
Those case requirements are tough. mATX is probably going to be mandatory. If you drop your HD requirement down to two drives, then you open up a wider range of cases. I'm looking at this Silverstone for a possible build. It's actually smaller than your dimensions, has good cooling, and should have no issues if you ever want to toss in a long high end card.
Others have mentioned the CPU, motherboard and Optical drives already, and they're basically the same suggestions I'd make.
*This usually never happens, but this time I feel he's incorrect.
Also, while SPCR are useful for quite a few things, their failure to test any PC P&C PSU's make them useless for a direct comparison.
As a long time Turbo Cool owner, yeah, they're loud as hell stock, and I can understand why it causes what I see as knee-jerk reactions even when you don't mention Turbo Cool at all. And the earlier Silencer models weren't silent, although they were not loud per se; they were silent compared to a Turbo Cool.