immense shoulder and tricep session lance:) shoulder press is strong as hell, and u made the right call bumping up the weight, i agree that progressing from 4 may be abit hard. maybe consider bumping up the weight by 2,5 kg instead of 5? cuz 5 is pretty significant for an exercise like shoulder press where ur not using immense weights like u do on squats and deads.
also, good call about not doing back when ur legs were not ready. actually i would consider moving ur split around so u get more time between working legs and back, both to let the legs recover and also ur lower back:) maybe legs on day 1 and back on day 4?
as always good work and look forward to tonights session