I know this is a old thread but, I just found out that my video card in the x51 only draws 125 - 150watts so im assuming a 330watt psu does just fine. Besides, after owning the system for almost a month I can safely say it's a good buy.
Only con: Download MSI Afterburner so you can tweak the fan rpm for the gpu, the gpu runs a little hot at 70c. Tweek afterburner "fan speed (%)" to "auto" and click on the "user define" option. Your gpu fan will run at a higher rpm but keep the gpu nice and cool.