Yea I "kinda" have tried different doses. 300 mgs at one time, makes me go haywire and jabber on and on lol and then shortly after, I crash, get irritable, then cant sleep at night, and get even achier.
I've nvr really used much of anything, besides food

and vitamins (Omega 3, 6, 9, multivitamins), and protein shakes. And most of my life, I grew up drinking juice, water, and a lil Koolaid now and then

so I guess my caffeine exposure is minimal.
Done a few cycles on a preworkout (MRI Black Powder), stuff gets me JACKED! I think it only has 200-300mgs of caffeine.