The 6870 requires a 500 Watt or greater power supply with 24A on its +12V rail.
Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Continuous Amperage Available on the +12V Rail(s) is the most important factor
from Ko888 ^
The CX600 with 40A on its +12V rail is quite sufficient for your rig. SO is the GS500.
Even the CX430 with 28A, would be sufficient. But considering your FX4100 to be OC'd, which is quite power hungry,
the CX600V2 would be a better/safer option.
This PSU features Active Power Correction, has efficiency greater than 85%, delivers 40A on a single +12V rail and has two PCI-E connectors. It is modular too and I think it will be cheaper than Corsair 600w PSU.
This PSU will last for years delivering continuous and reliable power supply to your system.
But I still don't understand why really below 600W is enough because I filled a test for how much Continuesly Watt I'll need for my build and it said 588. Thats why I am looking at this: (And can you tell me how much Amp there are @+12, couldnt find it http://www.dustinhome.dk/product/5010462266/ocz-modxstr...