love_sex_desire
Bluelighter
Note that I'm only talking about the psychedelics that I have tried (except mescaline and DOx, but these I do not need to try to know they last for days).
What makes you think mescaline lasts days? Mescaline lasts about as long as LSD. Some people in my city (central Canada) have a misconception that mescaline is an insane trip and lasts days, but I think this misconception is due to the fact that some people are sold datura as peyote around here. A few people I know, myself included, were offered "peyote" that was actually datura seed pods about 6 years ago, maybe longer. This explains why people think mescaline is so fucking insane, because, well, datura is FUCKING insane!
I like your method of elimination

2C-I is probably a good starter, but I simply was never that impressed with it.
LSD still gets my vote, al though the duration could be a problem if someone was unfamiliar and uncomfortable with the psychedelic high so I suggest having a benzo on hand.
OP: Have fun!