I haven't taken CK yet, so I'm not really the best source of information. But in my path for studying, I'm not using Step III resources for Step II. I've allotted myself quite a bit of time to study for Step II, so I've read through a few of the reference books. Crush and its Brochert-authored clones are good books to begin with, to give yourself a foundation. The Kaplan series is a long read that (aside from OBGYN) seems to break things down nicely. First Aid is very dense information that seems good to finish off with. UWorld is a must.
I started with consistent 43%'s in USMLE World back in May. After reading Crush and the Brochert clones, I moved up to 56-59% into early-June. By late June, I was getting consistent 65%'s while going through Kaplan's books. I'm halfway through those (finished OB and Peds, in the middle of IM) and am getting steady 75% (with variance -- I've slumped to 56% and have risen to 81%).
The way I figure, lots of people have taken this exam before us and have done very well. Why mess with proven methods? My uneducated advice is to prioritize your time and make USMLE World your most important resource, with First Aid as your guide if your time is short. Judging from your previous post, you seem to be kind of anxious about whether you're studying the "right" resource. Having read through some, there's a lot of overlap. Don't stress just because you didn't read a library. Just study something notorious and hope for the best on test day.