if you want epic stream practice, go play dragonforce songs lulz. (like the one in my signature lololol)
I have a regular rubber dome keyboard, but i still can get up to like 240 bpm streams (tho i can't hold it for that long) and like 135 ish bpm single tapping, but not for that long either. it really just comes down to stamina, and how you press down your keys. obviously smacking them down as hard as you can is going to make you tired. It's harder to be able to use just enough force to push a rubber dome keyboard down to register it, but one should strive to get as close as possible to that. If you have a mech keyboard or something, well, idk what to say... just keep practicing. idk how mech keyboards feel either so yeah.
idk how much my like 10 years (or something) of piano helps me, but it definitely helped a lot i would assume. basically, it comes down to practice.
also, i usually have my wrist down on the table like almost all the time, unless i'm like trying to spam as fast as possible. But, I'm pretty sure having your wrist in the air will help stream steadiness and speed, but it's just tiring to have your wrist up like that and if you are not used to it, it's just extremely awkward. It never really worked out for me, so i just stuck with resting my wrist on the table.