Hey, I'm not sure what's going on with you but we have very similar stats so I thought maybe you can consider - I took the exam already last week.
UW first pass (3rd year) - 61% overall
UW second pass (6 weeks of studying) - 67% overall (last 6-8 average 71%)
NBME 4 - 200 (about 3 weeks before)
NBME 6 - 225 (about 2 weeks before)
UWSA - 242 (1 week before)
NBME 7 - 223 (3 days before)
Obviously I don't have my scores back yet so I don't know how I did, but I think usually UWSA > NBME for most people. I combed through a huge list of scores from several different forums to see if I should take my test and it seems like people have gotten similar NBME profiles to me but UWSA ended up being more predictive. I'm ok with 230's also so I went ahead and took it.
There's something strange going on with your UWSA. Did you take it under different conditions? Were you fatigued? If you are getting 69% cumulative the UWSA shouldn't seem to be super difficult. I found most of the question much easier than the UW normal questions. What's your last 6 block average in UW? In your second pass, did you recognize a lot of the questions?
I've seen from many threads that if UWSA is roughly the score you want, you should go for it, but I don't know why your UWSA is so low - either that is low or your NBME 6 is inflated. Similarly, how did you feel when you took NBME 6?
There's a few ways I think you can go about doing this. NBME 4 is very predictive, and so is the Free 150. Study hard for the next 2-3 days and take either the NBME 4 or the Free 150 as you would the actual thing. See which exam (NBME 6 or UWSA it's closer to). If you get >80% on Free 150, you will pass as long as something catastrophic doesn't happen, so you can also use that as a confidence booster. Just don't use up both resources early if you think you will postpone. NBME 7 is really hard and has really strange questions IMO.
I think you probably should be ok to pass given your NBME 6, but I'd hate for that to actually be a fluke and you're doing more around your UWSA range. You are in danger if that's actually your baseline, but based on my own performance and your UW average I think you probably should have a good base assuming your UW average isn't artificially inflated either...
Bottom line, you need to take NBME 4 or Free 150 to tell. If they corroborate with your NBME 6 and you think the UWSA may have been a fluke, then you should go for it.