Very different in feel and physiology, it isnt about potency.
Amphetamines give you a sense of excitement and fun... you feel them coming on by a sudden desire to do things and everything seems exciting.
Caffein you just feel your heart race, maybe more awake, more energy... but not much in the way of excitement, motivation, or really anything from an emotional perspective.
Caffein makes me awake but makes me wish I wasnt (because i still want to sleep).. amphetamines makes me happy im awake.
@thor @realcaseyrollins
Also, youmay find this interesting... I have almost 0 tolerance for caffein. I can drink it and i wont die, but if I do I find it generally unpleasant. It lasts forever for me and I cant sleep at night even if I drink it in the early morning. On the other hand amphetamines make it easier for me to sleep, assuming i took it early int he day.