New computer with enough PSU

Hey all,

I'm looking at building a new computer with:

AMD Phenom II X3 720 2.8GHz
GIGABYTE GA-MA790X-UD4P
Kingston HyperX 2GB
Either a 4890 or a 4850 X2

I currently have a 550W PSU with decent rails from Thermaltake and I was planning on just using that in my new build. My question is do you think that this is enough? (please don't give any recommendations for anything over 650W. It's a computer, not a third-world country)

Thanks.