The 525 is an old part number. I dont believe EVGA still makes that one. I would get the card from Newegg, see how high it is by default, then OC the thing and see how high it goes. If the default is less than the advertised 450 core, AND the card wont OC well, send it back for the advertised clock speed version 528+ versions.
As for the KO question, that is a better EVGA version that they sell with even higher clock rates. Their standard GTX version is already OC'ed but their KO's have a larger heatsink/fan combo and thus more expensive as well. I own two KO's and one Non-KO and truthfully I can get them to clock about the same. The KO's I have are running watercooling though and so they edge out the air cooled non-KO by about 25 on the core, and 40 on the memory speeds... But my non-KO gets up to 525Mhz core/ 1.42Ghz memory, so I am not complaining...