@K there's definitely a difference in difficulty on PTs I've been taking. A more obvious variance in the modern ones too, in my opinion. I find the scale to be kind of unfair usually, so I try to improve my raw score, in general.
studying yes, PT no, because you don't get to use earplugs during the actual test. so better to download JY's awesome 7sage app and to simulate the real test by using "white noise" and "distraction" functions :)
For three LR section, I am pretty sure which one is the experimental section because the second one I took has one stimulus but two questions (Q9-Q10), which is certainly not the modern LSAT style(after PT60s)
I have recently wondered the same thing and I feel that maybe recycling a section from old PTs is a good way to not only accurately simulate test day with 5 sections, but also to help you review.
@synergy_101 already listed some but if you want challenging LG's in general, do the ones from the early 1990's. For some reason, the logic or at least the wording appears a bit more complicated than the "modern" LG.