I just finished all old NBMEs. It wasn't something I had planned, but I'm engaged in some family issues right now, and thought it a better alternative to completely stopping studies.
My mistakes range from 0-8. I dropped some very easy questions, probably due to being somewhat distracted while solving them. For someone like you, I dont believe old NBMEs will offer much. I can't really say if they benefited me at all. Their language is similar to that of newer NBMEs (vague/tricky), so for people having trouble transitioning from UWorld to NBMEs, they might help. But this wasn't the case for me.
I think this close to your exam, and considering your level of prep (I'm guessing you have more material to cover than most people), you should probably skip them. Not sure if you're planning on repeating UW incorrects or redoing all of it, but you do have all online NBMEs, UWSA 1 and 2, as well as the free 120. Thats more than enough imo.
To answer your question, I found them easier than the newer NBMEs overall. However, once you get into the 180+ range, you're down to those few questions that anyone can get wrong. The 180 I easily got correct in the old NBMEs were, on average, easier than the 180 I easily got correct in the newer NBMEs (16, 17, 18 etc). But my total no. of incorrects is similar between old and new NBMEs. But to be fair, I was MUCH more focused in the online NBMEs.
If you're consistently getting >190/200, I think you're set for a 260+ score. I hope I am too! The 1.4 multiplier is inaccurate, because the multiplier changes as you score higher. Once you're >190, its accurate. For someone scoring 170, he/she should probably try multiplying by 1.3.