Interesting delema you have because the settings on the two cards are different and while you can overclock a card the one thing you can't change is the Cuda cores , which the 570 has 32 more of. When you have a fqactory overclock all that means is that the card is overclocked before you get it and there is not much room left for overclocking while the reference card is not overclocked so there is more room to go but they will both end up at the same top end.
My choice is the 570 because it is the stronger card and it starts off with more cuda cores and if you are ok with overclocking then you should get more performance out of the card.
If your not comfortable with overclocking then the 560Ti 448 would suit you better. Evga has released the newest version of the Precision software and it makes it easier to overclock and monitor the cards.