If that site is what i think it is (which i can't tell because it won't open) It is very inaccurate. It is always better to go with a higher rated psu because that way, it is not working as hard, therefore prolonging it's life span. If you use all 460w of a 460w psu, you can expect it to last a no where near as long as a 600w at 460w. Plus if you ever want to SLI/Xfire, you will need a higher rated PSU. It will last you quiet a while getting a good PSU.
I agree about the site being inaccurate, but it is the best calculator out there unfortunately. I would recommend getting a PSu larger than you need, due to the effects of capacitor aging. For that build I would recommend this PSU:
It has plenty of power to allow you to upgrade other components later. There is a 500w version for $10 less, but I find it kind of pointless. In general, it is recomended that you buy PSU's made by Seasonic, Corsair, antec or some of the XFX PSU's.
I would also try and spend a a little more on your graphics card if this is to be a gaming rig, try for at least a 650ti:
As I said above, It's recommended that you buy PSU's from a choice few manufacturers, as they are the only ones who reliably produce PSU's that actually perform as stated. Seasonic, Corsair and Antec are the only brands I buy, but a few people have recommended some of the XFX units, but only the ones produced by Seasonic. A lot of the Corsair PSU's are made by Seasonic.
I'm building my own desktop and I'm pretty sure I'm going to use a 460w power supply. Would a 600w ever be necessary if I'm not trying to build a "beast machine"?
Get a new power supply psu with a high efficiency power. I much prefer a platinum one. It has a 90% efficiency power. A <a href="http://www.***/best-power-supply-psu">new power supply psu</a> can build you the best machine.