Most power supply calculators overestimate by a gross deal I've found out, but only because a lot of power supplies only produce their wattage at 25C or something like that (lab conditions). It's better to assume the PSU will operate at 40C. In any case, I've put in a Kill-A-Watt on four builds and found out that even under a nominal load like a game, power supply calculators are often over 150% to 200% what really seems to be a sweet spot (double that of a nominal load, because most PSUs are most efficient at 50%).
The only time in my experience that I've ever, truly maxed out my hardware is if I ran Prime95 and Furmark. Some people will say just get the biggest one you can afford because you use less wattage, it's happier, and you have room for future expansions. If I were to play that game, then honestly people should be getting kilowatt power supplies then if they can afford it. And future expansions are only a concern if it's another video card.
So this latest build I have is putting all the data I gathered to the test. It's more or less a high-end gaming rig with a 450W PSU. And it still doesn't pull more than 230W when running an intense game.
In any case, I also use http://extreme.outervision.com/psucalculatorlite.jsp
. Though I think everyone else bases their calculators off this.
I also don't believe in going overkill in anything except hard drive space (because I'm a packrat). The problem is that sure, you can afford it now, but you never know, you could've spent the money on other things. If you make informed decisions on your hardware choices rather than just plugging in higher numbers, you have less of a chance of making a regretful purchase. Because from what I see, you could've spent say... $300-$350 for this build and it would still be sufficiently powerful for your tasks. What could you have used that extra $150 for?