Is 600W overkill for my system?

Hello,
I have recently built my first computer and today I bought a graphics card - the Sapphire HD 6870:
http://bit.ly/vZbHNA
My current PSU is a 500W CIT that came with the case. I understand that it is not worth the risk of keeping a crappy PSU so have decided that I need to upgrade my PSU as well.
Can anyone recommend a good PSU for under £50?
The rest of my specs are:
ASUS M4A78LT-M LE
http://amzn.to/z1CeXo

AMD Phenom II X2 560 Black Edition 3.3GHz
http://bit.ly/AkBmJM

4GB of 1333mhz RAM

2x Western Digital Caviar Blue 160GB
http://amzn.to/xSQo9g

Sony Optiarc DVD drive
http://amzn.to/wlUM68

Thanks in advance!
P.S. What do you guys think of my components? Bear in mind I'm only 15 and it's taken awhile to save up for this - so be nice

http://www.hardcore-games.tk/wp/psu.php

I suggest a 650W model for the gear I see ^^^^^

for £50 something like this

http://www.aria.co.uk/Products/Com [...] ctId=44572

or if you can stretch to £70

http://www.aria.co.uk/Products/Com [...] ctId=43905

500watt good PSU will be plenty for OPs rig I run same CPU unlocked to a Deneb quad OCed @ 3.6ghz, HDD 3x, and a far more power hungry GTX 275 GPU and it all runs just fine on a mediocre Cooler Master 460watt PSU that only delivers 420watts effective.

XFX Core Edition PRO550W - 5yr warranty
http://www.ksn-online.com/products [...] 822&info=1