OC means Overclocking - tl;dr Increasing the clock frequency above the "standart" set by the manufacturer to increase the performence. For example, my FX-8120 comes with a base frequency of 3.1Ghz, I overclocked it to 4.8Ghz and it has increased my performence tremendously in games that are CPU heavy.
CM is running on pure CPU power, the GPU does almost nothing, atleast in my case I never get more than 12% load with my 3(?) year old at-the-time already mid-class HD7870.
Intel Core i5-4690K is just what I would recommend, what motherboard do you have in mind?
The 660 is a budget card, won't stand many modern games (assuming 1080p >medium settings) but is still overkill for CM.
I would strongly advice against a laptop, even if you find one with the 4690 in it you won't be able to overclock it without having to flash the BIOS (I have never seen a laptop with a fully unlocked BIOS out of the box). And even if you do that the laptop won't cope with the heat, that's why you'll probably get the cpu downclocked by the manufacturer to keep the heat level managable with those tiny little fans in that tiny plastic box. It's simply not possible to fit something like this into a laptop case => you gotta throttle the "engine" so hard that it generates just as much heat as those laptop fans can take.