Raidmax is a Tier 5 PSU, not reccommended!!
What CPU do you have at present? Even modern games do not use more than 2 cores properly, so you will not get twice the performance by going from 2 to 4 cores at the same speed.
I am running my older Phenom 9850 b.e, @2.8ghz , Jetway H0A4 extreme motherboard, 500 gb seagate harddrive sata II, and 2 gb of ocz reaper 1066 ram, a 3870 card and a NZXT tempest case with 6 120 mm fans of a Antec 550 watt power supply and have not had any issues even with overclocking the 3870 and 9850 b.e. I am not sure about the Quality of your PSU, but I believe it can handle the wattage if it holds up and puts out the wattage it says it can.