yes, same goes with your setup... you can have the "best" equipment (desk, chair, monitor stand, keyboard, etc...) but if you are not following good ergonomics or have bad typing/ergonomic habits all the fanciest equipment in the world won't be able to help you.
i was commenting in a thread about this the other day. person had an expensive setup and was having pain issues. turns out it was just their posture that was causing the issue.
muscle-memory... i know. i was thinking the same thing. i also thought it would be hard to go back to a standard board (or laptop) after using a split ortho for so long. again, turns out that's not the case. probably because i'm not using some kind of alternate keymap like colemak, dvorak, workman, etc....
if you're looking for performance... what you know the best and have used the most will give you the best performance.
- i use an alternate keyboard because i can do some things with it i can't do on a more common keyboard. (numpad layer, more comfortable chording key commands)
- same goes for my mouse, not so much the form but more the function. i have a couple now that are totally programmable in the way that you can use keyboard codes/actions in the mouse firmware. one example is i have the wheel button as "enter/return" so i can quickly get through prompts, etc. without taking my hand off the mouse or mousing over to the "ok" button.. sounds simple and silly but makes a big difference in what i do.