Based on my analysis, the OG 13th
edition difficulty breaks down like this:
Problems Composite Score Level
First Third 500
Middle Third 550
Final Third 650
These divisions apply to each problem type in the OG. A 650 composite score means that a student is getting half of the problems at that level correct. So, if you are acing the final third of the problems for each problem type within official timing limits, then you are actually performing at a level higher than 650.
This analysis comes from my guide to self-study: GMAT Clarity
As per now, I solved 0-100 numbered questions(Problem Solving) yesterday, I had 95% accuracy at the problems and solved each question in around 50-90 seconds. So, what do you think?