Well, I thought I take the easy way out and ask if anyone here knew the answer, but no takers...
I checked the USMLE.org site and they say:
"On the three-digit scale, most scores fall between 160 and 240. The mean score for first-time examinees from accredited medical schools in the United States is in the range of 200 to 220, and the standard deviation is approximately 20. Your score report will include the mean and standard deviation for recent administrations of the Step."
That doesn't help too much, but I guess it means that it's basically the same as for Step 1.