Maybe it's an option for you. You can't assume everyone is willing to damage and/or void the warranty on their gpu. The question was which one to get. The 570 is a better board in any scenario. He didnt ask which card was better bang for buck.
Okay, I give you that one... The 570 is the better card between the two he posted up.
However, being that this is a technical forum, we as members would still like to inform the OP about both of the cards, their capabilities, price to performance ratio, and so for. The OP may not have asked which card was the better bang for his buck, if he cared about voiding warranty, and/or etc... but it's still in his best interest to know all of this info so he could at least have knowledge of what he's getting himself into.
OP, here's a good read if you want to know more about the 448 cores:http://www.tomshardware.com/reviews/geforce-gtx-560-ti-448-core-benchmark,3082.html
Good luck with whatever you chose.