I think some of the confusion when sizing power supplies is that caused by a failure to understand just what is going to be on what rail, if the P/S is multi-rail. You have to be careful to avoid overloading any single rail, and sometimes just determining if you are likely to be doing so can be tough - especially "can't see it because I haven't bought it yet". So sometimes the easy solution is to just "overpower" it and be done.
Take the Seasonic P/S in the hardware list posted - it's a 2 rail P/S, both rails rated at 17 amps. I can't find a wattage rating on the MSI site for video card, but no matter how you combine a high-end video card, a processor, motherboard, and drives, you are likely to top out one of the rails if you only have 2 - and what's worse, nothing I saw in the Newegg listing gave me any confidence that you'd even be able to determine which connector is on which rail.
Personally, I like the single rail P/S's - they take 80% of the guesswork out. The problem is, I don't like what they generally cost.... And so going the other way - A 4 or 5 rail P/S where every connector "strand" is generally on it's own rail is easier to deal with. What I really don't like are 2 rail P/S's, because you can't usually tell what's on what, and you end up doing too much "guessing and hoping".
And nothing, nothing makes a system more flakey than the instable voltages that result from an overloaded P/S rail...
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