Difference between most expensive 670 and cheapest worth it?

I'm in Australia.  

What am I going to get as far as fps is concerned in 1080p max settings (say, Crysis 2) 3D vision for $125 (the difference in price) after over clocking in a reference card and one with an after market cooler?

These are the two cards in question:

Galaxy Geforce GTX 670
http://www.pccasegear.com/index.php?main_page=product_i...
$399


ASUS GeForce GTX 670 DirectCU II or EVGA FTW
http://www.pccasegear.com/index.php main_page=product_info&cPath=193_1387&products_id=20212
or
http://www.pccasegear.com/index.php?main_page=product_i...

$529


Also the reference EVGA, which is $479 ($80 more than the Galaxy) on this site.

Especially if I put two in SLI, there's going to be a price difference of up to $250. What kind of performance increase will I get (after over clocking) in the more expensive 670s compared to the cheaper one for that?