If it comes with the same cooling the boost should stay the same as the overclocked version. So to speak, the overclock won't matter.
I've owned 2 different GTX 660, one by inno3D which was with a aftermarket cooler and a Little bit of oc, it went to 1084 MHz on boost. It had faulty cooling which was making the GPU hit85 degrees. I then got a GTX 660 by club3d, this Card was with the reference cooler and at stock speeds. Because of the better cooling (it only gets 70-72 degrees)at boost it reaches 1110,5 MHz. It all comes Down to how hot your GPU will get and then the GPU will overclock itself as fit.