Agree with everybody else -- take 6 in addition to 7 and Free 150. I actually took 7 and the Free 150 in one day, to simulate a full-day test. The Free 150 are definitely easier than the other NBMEs (but still worth taking) so I would save those for last to boost your confidence before the real thing.
1nycdoc, after 6 and 7, my opinion is that it doesn't really matter which of the other NBMEs you take. They all have their strengths and weaknesses. NBME 5 was one of my lowest scores, but other people have said that the questions were not as well written. Whatever. I'd probably take 5 over something like 1 because it's more recent.