You need a strong psu though. If you have a crappy one, it wont hold and wont give enough power to the system causing performance loss. PSU is the most important part of a computer.
ahh, thats where you are wrong. If you are overclocking to the extreme with SLI/crossfire, then your psu will be stressed. A Powerstream 520 has a max wattage of 616 watts and thats when its fully stressed. I know people have needed more than that.
Try removing two sticks of RAM and ocing that FX. That should get you a higher score. Right now, you are really really stressing the memory controller. You might even be running 2T.