No one can answer that question reliably (with the exception of the people who actually write the GMAT scoring algorithm). I can only guess, but my personal gut feeling is that the 5 or 6 missed at the end depends on how you are doing. Imagine if you are not doing well at all, the last 4 or 5 missed won't matter quite as much since you're already doing bad. But what if you were doing really well then missing the last few in a row - well that seems like it would punish you more. However, in practice, on my practice cats I found that to be quite the opposite - even when I missed a few at the end as long as I was doing well throughout the exam, my scores ended up decent. My explanation for that is that the algorithm takes into account how well you have been doing over the long term (you are consistently in the 700s throughout most of the test vs just hitting your first 700 question at question 38).

Of course this is all just my conjecture. Perhaps a GMAT instructor has more insight?