All factory OC'd cards are not created equal. Factory OC'd cards fall into two general categories:
1. Reference designs which they put on a small OC and which leave very little room for additional overclocking. You can get the same result by OC'ing these cards yaself.
2. Non-reference designs with beefed up PCB' and larger, more efficient coolers. Fortunately these costs little more than, if anything, over the reference designs
The reference design has a 4 phase VRM design. The EVGA model you picked has a 4 phase design and falls into category 1.
The Inno3D and Phantom have 5 phase designs which gives you a bit more to work with as it does just enough to sneak into category 2. The MSI Twin Frozr has a 6 phase design and a very good cooler.
Stepping up another notch is the Asus DCII TOP and Gigabyte 900Mhz design, both with superb coolers and 7 phase VRM designs. Hardware Heaven tested this board at 1070 MHz, that's a 30+% OC over the 820 MHz "reference" design.
http://www.hardwareheaven.com/reviews/1104/pg19/asus-geforce-gtx-560-ti-directcu-ii-top-review-and-sli-performance-conclusion.html
The MSI Hawk has 9 phases and the Lightning I think has 10 but it doesn't appear to have helped them to do any better than the 7 phase designs as I haven't seen any benchies showing any improvement after 7. Might be out there but I haven't seen em.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121425
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125363
Since October I have installed about 17 Asus TOP cards ...... every one of them is running at 980MHz or above.....16 of those were in SLI builds. I'm a bit more daring with cards in my own home and Son' No. 2"s I had originally at 1020 MHz .... turned it down to 980 when the warm weather hit. But with a recent PC cleaning and the new fan profile I set up after installing Afterburner 2.2.0 Beta 15, temps on the top card were only 75 (70% fan speed) so may scoot it up again.