That's actually one of the more expensive GTX 560 Ti's that I can see on Newegg. There is even an identical EVGA for $200 after rebate and free shipping:http://www.newegg.com/Product/Product.aspx?Item=N82E16814130623
(I didn't check, but i assume the warranties are different.)
I would take a closer look at Newegg and be sure to get one of less expensive models. The other choice for under $300 would be the GTX 560 Ti 448 cores model, which would be an even better upgrade for your 560.
A good 500 watt PSU is sufficient, so you are good with that Corsair unit.