PSU question

Hi,

I'm about to start my first system build, and I'm hoping to keep it as energy efficient as possible (more for moral reasons than financial ones).

E7200
Gigabyte EP35-DS3L
MSI 9600GT
8 gigs OCZ DDR2 800
640 gig WD Caviar HD
22" Acer LCD
Asus 22x DVD burner

this is all going into an Antec Sonata Designer case that came w/an Earthwatts 500W power supply. My question is how much overkill is that for the system? I bought the case because it was a great deal ($89 after rebate), but will it be running really inefficiently on this system? It's 80 plus certified, but I'm guessing that a 300W supply would do just fine. Is it worth swapping out the large supply for a smaller one?

a 500w power supply does not use any more power than a 300w power supply does when powering the same system.
http://www.hardwaresecrets.com/article/181
Keep the high efficiency 500w earthwatts.

The PSU might be more than you need but it has very good efficiency down in the ranges where your system will run.
PC Load / Eff % / Draw from wall socket (From: HardwareSecrets review )
193W / 87.7% / 220 W
295W / 86.5% / 341 W
You'll need a PSU that would beat those figures and that might be hard to do.

edit;
For comparison: Zalman ZM360 PSU Corsair VX450 * The Corsair is fractionally more efficient than the Antec EA500.