Well, by sets of 5x20 I can get a lot of volume 5x20x30kg=3000kg per workout (twice a week full body) with relatively low intensity around 60%.
That is my logic at least. After a month of 20-15 I plan to increase weight doing 5x12-10-8 reps for one month, and than again do some strength block with 5x5, 3x3 and singles as I am used to work.
Such volume is for OHP only.
I was surprised how quickly I ran out of fuel, since I took 24RM weight actually, thats 9 reps in tank.
I actually found quite different numbers on internet for 20RM, it seems it varies a lot. Some list 15RM as 60%, some 65%.
Will do as Strongmangoals suggest, use actual weight I can do 20 and use a bit less actually so I am not pushing to failure.