yes, split and hand separation will be the biggest change and improvement.
whether you go with split staggered, split ortho, or split columnar stagger will all just be..... well... "splitting" hairs. (ha, ha)
i don't have studies to link to but i can speak from my experiences.
- split is definitely the way to go. i've been in front of a computer for the last 26 years for work, got a split ortho in 2018 (i won't go back to one piece boards). the hand separation alone is worth the change.
- i have very little experience with columnar stagger boards. though, i do have an ergodash. i'm not a big fan of the ergodash or others mainly because of the thumb keys that usually come with columnar stagger. while i whole heartedly believe that modifiers (control, alt, shift, etc.) should be towards the center of the board and not mandated to your pinkies. i found the thumb clusters made the stretches for commands/shortcuts harder/further away then how they were on my current board (keeb.io viterbi)
- i do more shortcuts/commands during the day than actual typing (designer) so my use case may be different than most.
- 14 column can be setup extremely close to standard qwerty (as a transition to alternate layouts, ortho, etc., not speaking to qwerty as far as efficiency of a layout, that's a whole other ball of wax.) with 14 columns you only have to move one or two keys.
- your posture and desk/setup ergonomics have more to do with "keyboard related pain" than staggered, ortho, columnar.
hope this helps, answers some of your questions.
feel free to ask me if you have questions i might be able to answer.