In the squat, what is too heavy to train with and too light to train with? In Russia , much research revealed that 65-82.5% of a 1 rep max is best to build strength in the squat. They suggest 2-6 reps per set.
At Westside Barbell we do sets of 2 for 2 important reasons. One, more than 2 reps tends Cause bicipital tendonitis and shoulder discomfort. This pain is commonly felt while benching but, in fact, comes from squatting. The bar shifts to some degree, causing damage. Having your hands spaced too close on the bar may also be the culprit. Two, in a power meet, we don't do reps so if we do 12 sets of 2 reps we are getting 12 first reps per workout. If you do 4 sets of six reps, then you get only 4 first reps.
This is closest thing I was able to find. The site was reorganized after I visited it last time and many PDF articles are in HTML format.
I highly recommend Westside Barbell, because it operates using principles, not the hardwired percentages and prescribed exercises. You can build your own conjugate system, for your goals or abilities. I did.
What kind of rest period do these use between sets? And do you have data on rep form decomposition at 5 vs. 3?