Building a new system,Opinions please.

[Xenosaga]

Actually, a good 400W PSU will handle almost any regular, sensible gaming system (e.g. a 4570K + Radeon R9 280X) for years to come.
Seriously, people tend to massively overestimate a system's power usage and buy either overpriced PSUs that yield no advantage whatsoever or $25 750W PSUs from ebay which equivalate timebombs. If you do not have any definite plans on going SLI/Crossfire, there's no reason to go over 550W.

Let's put things into perspective: A system consisting of an overclocked Radeon 290X, which is one heck of an inefficient, power-hungry beast plus an overclocked i7 4960X draws 400W from the wall. Of course, although a good 400W PSU will be able to handle it, you want a few reserves. Thus, a good 550W PSU would be more than sufficient, even for a beastly system such as this.