Someone in this forum said a while ago that, if you want Q50, you have to hit 99% in the first third, 95% in the second and no less than 90% in the third (of course, we are talking about problem solving from OG11). Maybe this was a little exaggerated but not far away from truth.
My hit ratio was approximately 95% in the first third, 90 in the second and 85 in the third, with figures closer to 80% in the last (and of course hardest) 20-30 questions. On the real exam my Q result was 48.
Definitely, there is a very strong correlation between your hit ratio on the OG questions and the real test, but remember, real test is adaptive which means that your score could deviate significantly, mostly due to your performance on the first 10-12 questions.