Your post doesn't make it clear whether you are talking about the Kaplan Home Study Notes, which are sold on the Kaplan website, or the Kaplan Lecture Notes, which are only available through a Kaplan course (unless you pick them up off ebay). In either case, however, each is sufficient. I personally thought that both were better than Lippincott in getting straight to the point. But I guess it depends on your background. If you already know the basics, then Lippincott is overboard in my opinion and takes too long to get through when you only have 4 or 5 days to review Biochem in the month before your boards. (Actually this issue of being too much applies even if you don't know much biochem. It only fails to apply if you give yourself a few weeks to really work your way through the book. But that would be shooting yourself in the foot, if you did it at the expense of the more important step 1 subject areas.)
Every student I have spoken to has said that the majority of biochem that showed up on step 1 was woven into other subjects areas, particularly path. It's uncommon to get pure biochem problems which are not clinically relevant to medicine.
So, yeah, Kaplan's Q-book (not bank) says that biochem makes up 12 or 13% percent of the test but the percentage of pure biochem questions (the ones you couldn't answer from knowing related path, phys, or micro) is surprisingly small. Most people said that they got maybe a handful at most, as in fewer than 5. So, that's not something to sweat.
I should add in the customary caveat that everyone's test varies, but I'm sure you already knew that.
