The factory OC'd 560 Ti is an easy choice, especially in SLI as it provides the best bang for the buck (cost per frame) of any card > $200. It's half the cost per frame of a 580 or 7970.
Guru3D uses the following games in their test suite, COD-MW, Bad Company 2, Dirt 2, Far Cry 2, Metro 2033, Dawn of Discovery, Crysis Warhead. Total fps (summing fps in each game @ 1920 x 1200) for the various options in parenthesis (single card / SL or CF) are tabulated below along with their cost in dollars per frame single card - CF or SLI:
$ 160.00 6870 (434/701)
$ 0.37 - $ 0.46
$ 220.00 6950 (479/751) $ 0.46 - $ 0.59
$ 240.00 6950 Frozr OC (484/759) $ 0.50 - $ 0.63
$ 205.00 560 Ti (455/792) $ 0.45 - $ 0.52
$ 320.00 6970 (526/825) $ 0.61 - $ 0.78
$ 205.00 560 Ti - 900 Mhz (495/862)
$ 0.41 - $ 0.48
$ 340.00 570 (524/873) $ 0.65 - $ 0.78
$ 500.00 580 (616/953) $ 0.81 - $ 1.05
$ 725.00 6990 (762/903) $ 0.95 - $ 1.61
$ 750.00 590 (881/982) $ 0.85 - $ 1.53
$ 450.00 7950 (603/NG) $ 0.75 - ERR
$ 550.00 7970 (675/NG) $ 0.81 - ERR
I don't know what gives rise to the notion that you can take a stock reference GFX card and boost it up to the same levels as the factory overclocked non reference designs. Ya would think the fried 570's fiasco would have shaken this mindset from the community consciousness.
http://www.overclock.net/t/929152/have-you-killed-a-570-no-recent-deaths-buy-some-570s/550
Yes, you can probably take a reference card and pop it up to the levels of a factory OC'd card "outta the box". But factory overclocked cards with larger coolers, and beefed up VRM's will reach levels that reference cards can not.
here's 1070 MHz...reference is 822 so that's a 30% + OC.
http://www.hardwareheaven.com/reviews/1104/pg19/asus-geforce-gtx-560-ti-directcu-ii-top-review-and-sli-performance-conclusion.html
The main difference between the Frozr II and the Lightning is the number of VRM phases. The Frozr II has 6 phases.....the cards know for hitting the highest overclocks have 7 or more. IIRC, the Hawk has 7 and the Lightning has 8
I have had great success with the Asus TOP models, none of which has failed to reach 1000 MHz
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121425