Shows a system with an i7-965, which is much more power hungry than any Sandy Bridge CPU using 312W at the wall. Take 10-20% off 312 to get their actual system power draw and I think you have a somewhat realistic worst case for your own system's maximum power consumption. Depending on what programs you run I would think your typical consumption would be much lower.
A ~280W load only stresses a 450W PSU to ~63%. So as long as you have a high quality PSU, operating in temps below its temperature rating then you shouldn't have any problems.