The 550 Ti only need 22 amps and both 12v rails are 30a. Problem is that PSU is one of the worst PSU's out there. I would not chance it with my 550's. I am sure asnorton 44 miss seeing the second 12v rail I almost did.
Good job VetteDude. I would think about the fucture. What am I going to do later on? Am I going to buy a better card? which you will. the 550's are the weakest of the GTX 5xx series. I wish I hadn't got mine.
So if you are going to upgrade later on I would get the bigger of the PSU's shown. That way you are covered later on. All this is just food for thought. And I wish you the best on getting a new rig. Good luck to ya.