that's basically the same system I have... good choice with the equipment I have listed in my signature, at full load, the power draw is just under 220 watts (not including the 50watts for the speakers). Idle is just about 200 watts. 300 would do the job, but I'd also recommend a 400 watt because the less the load on your PSU, the cooler and more reliably it runs. I'd recommend Antec, Enermax, Vantec, or Ultra-X (what I'm successfully running)