I agree, the psu is very important... however I personally think that psu is enough for that build, but why limit your upgradability? If you buy a psu with 700+ watts now, you will have options later, and will most likely spend less money on your next build, as you will be able to use the psu in the future, or simply have enough power for upgrades, add a video card(Sli), or extra hard drives, fans, optical drives etc.