One piece of advice I got from
this slightly outdated article from RPS is this:
Bus width is just as important when it comes to memory performance on graphics cards. The rule here is simple. Touch nothing with a bus smaller than 256 bits. Anything more than that is gravy. Anything less isn’t worthy of HD gaming.
The cards you linked seem to have a bus width of 192 bits. In all honesty, that's probably fine, but it looks like you're trying to go as close to the bleeding edge of current technology without paying out the ass for it. It may actually be worth considering going for a 670 instead, unless you can find a 660Ti with a bus width of 256 bits. But if I were to choose from the three you selected, I'd go with #2.
With a few rare exceptions, you don't actually need more than 1GB of VRAM, either. 2GB will handle everything just fine (and will for the next few years at least), while 3GB seems like overkill and can potentially sap performance (from what I've read). I'd personally stick with 2GB unless you can find some good reviews for a 3GB card.
EDIT: Oh, to answer your first question, I'm pretty sure the K just means you can overclock it. Most things aren't bottlenecked by the CPU (Planetside 2 being a notable exception), so I wouldn't worry about it too much... especially with an Ivy bridge CPU, and if you don't need to do stuff like video editing regularly. But if you do video editing regularly, you'd want an i7 anyway, so... yeah.