Usually the graphics card manufacturer puts down more watts than it actually needs, to deal with different manufacturers, different psu's, capacitor aging, etc. You have a good enough power supply. You can use thermaltakes power supply calculator if you are really nervous. I would not use the adapter they give you for the graphics card, I would use the 6+2 Pcie connector directly on your power suppl. The adapter is for PSU's that don't have the connectors but meet the requirements, which are usually older ones.