I think you are right, that's an awful big load for a 550w psu. Even if it can handle it, which it should be able to, do you want to run it at that for any length of time? They do degrade over time especially if they carry a big load. I have a 660w platinum with my 290 and it's just about right but if I was to need a new PSU I would get a 850w at least maybe 1000w because I will at some point be adding another card and I am always upgrading.
10/22/14 at 12:01pm