I went from 230 on NBME 2 to 250 on NBME 4 in exactly 2 weeks.
I think it depends on what you are covering in those 10 days and whether you have covered it before or not, but I think 80 points or so is pretty reasonable.
I have heard that 1=5<2<4<3, but then again, it all depends on your strengths and weaknesses along with what you have and haven't studied when you take them. I have also heard of most people getting somewhere around their 2,3,4 scores (when they take them just before the test), maybe a little higher, maybe a little lower depending on how lucky you get on the big day.