Going by what your specs plus a bit over head i'd go for the 550 Watt PSU. I'd also go for a antec, FSP or cooler master. what ever it is make sure it has some weight.
I would get the 550Watt PSU. You do not know which GPU you will put in to your system two years from now. SSDs become increasingly powerhungry (server grade SSDs push up to 38 Watt) and you do not know what crazy peripherals you will be plugging into your system.
You could get away with a 450w, but as already mentioned, its nice to have some headroom that way the psu is under less strain when the system is under full load. Similar priced Gold rated 550w units:
I meant it in terms of: SSD power draw will become non-negligible (not criticial though) in the future because Server stuff has the tendency to trickle down to the lower priced consumer market.
You're estimated to use 338W and I always recommend a bare minimum of 150W of headroom. I say this because some systems can draw an additional 200W of power under load. With that said I would say bare minimum wattage is 488W but 538W is preferable. So I agree with the others on getting a 550W PSU. As far as brands go I prefer Evga, Seasonic, Superflower, and XFX.