Unless you're starved for practice, I would only do one or two of Kaplan's 6-11..I'm with jot - after 3 months of intensive studying I scored worse on test #8 than I did on my diagnostic - they aren't scored properly, and the answers weren't always 100% correct. Tests 1-5 are good practice, however. It all depends on your comfort level - the number of tests you take.
I took 6 full-lenghts, however ended up doing about 20 VR sections in all because I felt most uncomfortable with this section. Although I wasn't entirely aware of my improvement until test day, doing all those VR payed off. On the other hand, I could have spent more time on PS because my final score only went up 1 point from my diag 🙁 (from a 9 to a 10). So what could have potentially been my strongest section turned out to be my weakest because I didn't focus so hard here. Bio was a fluk - scored a 7 on diag. Didn't concentrate too heavily on it - scored a 13 on test day. Moral of the story - know your weaknesses, concentrate on them, however don't neglect your strengths either. That said, I think doing 10 practice tests total would be plenty.
Also, don't be compelled do take an entire test or even section in one sitting every single time. You need some practice doing this, but it can also burn you out. If you're getting sick of timing yourself, to prevent burn out, just work the passages and give yourself that added practice. Just make sure your coming in under the mark on time as test day approaches.
