I seriously doubt that your system power consumption would go above 400W under a Furmark type load, so no you do not need to upgrade your PSU.
There is even less need to upgrade PSU if you are going to be replacing your GTX 570 with a more energy efficient card, like the GTX 660 Ti or 670.
Okay, that brings another question to my mind: How come whenever I try to overclock my CPU above 4GH'z my PC does not get past the windows splash screen? I've read around and found quite a few threads saying the cause to be a lack of the PSU. Care to shine some light on this issue?
Thanks a lot for your input by the way! I'm leaning towards the 670 now.