"My school told us that about 5% of the class breaks 260 each year. I don't really trust them... does 5% sound right to you guys?"
SDN---50% break 260
Hopkins---maybe 15%.
Everyone else: 1%
Don't read much into SD, in non normalized data, SD data almost entirely reflects that range of 68% or so of people at +/- 1 SD...It tells very little about the scores outside of that parameter.
The last time NBME reported percentiles, 211 was the mean, 21 was the SD (231=84th percentile, 188=16th percentile), and 248 was 99th percentile. So you can extrapolate from that, obviously less than +2 SDs was over 99%ile back then, and they still don't normalize the scores so you can probably assume teh data lies on similar plane. It is a pretty safe bet that over 260 puts you in the top percentile or at worst top 2 percentile.