About your 4th point, this is something a head coach at my club pointed to me, a couple of years ago when he first saw me...He understood that I wanted to generate higher swing speed, but was adamant of me trying to go first through the ball more and only afterwards coming over the ball... He wasn't even sure if one should have a fully straightened arm at contact (although I think that it helps what the OP wants to achieve). You know what other minor factor might help imho? Using a heavier frame, i.e. I was watching closely (a while ago) someone with a K90 hitting against something with a very light frame and I think that the momentum alone of the K90 helped carry it more through the ball….