This will be my first build.
8gb DDR3 1600Mhz
AsRock Extreme4 Gen3
H60 (I've got lazy and decided on this against air cooling.)
There won't be a graphics card as virtually no gaming will be done, although I do have a fanless 4350 which I might throw in there (I read that the HD3000 out-perform that so that putting that in might be pointless).
Between 3-4 hard drives.
I've seen a CoolerMaster Silent Pro 600w (it's modular, which I quite like the idea of), excellent reviews etc, but after running the proposed system through a PSU calculator I'm starting to think 600w is way too much.
(The calculator recommended a min. of 282w.)
What do you all think, and if it is too much, what do you recommend?
Yep 600W is 'too much' for your system. I have an i5 2500k at 4.4GHz, 2 sticks of RAM, 2 HDD in RAID 0, H70 and a GTX 560 Ti and I use 440W from the wall running prime95 and furmark. just running prime95 (which is about the most stressful/power consuming thing the CPU can do) it uses 180W, so add the 80% efficiency into it (roughly) it uses 144W, call it 150 for the extra hard drives.
So back to the original questions, you should be using a max of 150W on your PC,
looking at the efficiency curves of PSUs (just generic curves) your PCs load would be drawing at a pretty un-efficient percentage (PSU efficiency seems to drop rapidly below 20% usage) If you care about the environment then I'd get a smaller PSU, if not, well keep your current one!
So that you have the power later if you want it, I'd get a high quality 450-500W PSU. Gold rated if possible. That will allow you to use your computer now, and even add a good GPU later if you need it. And the gold rating will help you use less power, even at lower power draws. (Gold rated PSUs need to be 88% even at only 20% of draw. For a 500W, this means 100W.)
I never even knew that those top two even existed. In the UK the EA-380D seems to be the lowest wattage "quality" models around on the popular PC websites. are they hard to find in the US?
Well you learn something new everyday don't you
You guys are ace.
I'm thinking either the Corsair CX430 v2 or the Antec EA380D.
Similarly priced so I guess it'll come down to what cables/connectors they come with and what I need.
Just to throw a spanner in the works. http://www.newegg.com/Product/Product.aspx?Item=N82E168...
Apparently it's a SeaSonic S12II/M12II in a white case.
Like I said in the op, I quite like the idea of a modular PSU, although, I understand that they're pretty much all aesthetic over any type performance improvement.
Did a quick search for both of the SeaSonic units mentioned by Rugger, nothing in the UK. U.S market only type thing I guess.