Very interesting topic right here and I think there’s not much to add (unless you try and sum up progress reports from big gainers and find the common denominator).
However one unspoken yet important part here that I didn’t spot yet is Technique. Comparing this to bodybuilding, a bad technique does result in gains initially, but in the end it causes injuries. Therefore, there might be a correlation between total gains and times injured. (I know this is a bit off topic)
Did you guys consider split routines yet? (e.g. 2+ shorter sessions a day)
As for myself, I’ve gained around 0.5-1in in length using only manual stretches following J123’s Linear routine.
I’ll be following the thread closely!