I have close to the exact same build. Cooler Master HAF 932 instead of Antec 902 and 4870 1gb instead of 4890. I have my 920 oc'd to 3.2 ghz and I only have an Antec NeoPower 650W PSU. You should be fine. I will also slap down a vote for Antec PSU's. I have had mine for nearly 2 years and not 1 problem. Plenty of power.