I am only familiar with Step 1. That said, I don't know what the absolute lowest or highest scores are, or how these scores are calculated. It's pretty cryptic.
There's a 3-digit score and a 2-digit score. The passing 3-digit score is 185, national average is around 217, sd=20 (approximately). I've heard of scores in the 280's, but I think they are very rare. To me, anything above 260 is insanely high.
The 2-digit score is not a percentage correct or a percentile. All I know is that it's set to where 75 is a passing score, and it maxes out at 99.