OK I did some tests regarding power on my main PC. I have a Kill-a-Watt meter, so while not being the most accurate it will work fairly well to see how much power my computer is using.
It uses 0 watts when off, around 130 during boot, and 70 while writing this post. I ran 8 threads of Prime95 and a Furmark Burn In Test at the same time and my power draw at the wall hovered around 390w. Yes that means that I'm basically maxing out my PSU.
However, realistically when am I ever going to load all cores of my CPU to 100% and load my GPU up realistically crazy like that? Never!
So, given that it's a Seasonic, it's 80Plus Gold Certified, and I will keep everything clean and not dusty, It will be fine