I fit in the category of people you're alluding to. I have only done MDMA, coke & some ADD meds, and, to me, 4-FA has properties of many of them. I like it a lot!
Believe it or not, the highest dose I have taken is 55 mg. When I started out, taking like 40 mg would give me very noticeable mood elevation. Hell, I would feel just high, in general. When I first took it, I would have at least a good 2+ hours of incredibly energy. I couldn't even sit still.
Now I have upped the dose to 50+ mg (*gasp*!!), after having taken it almost every single day for like 10 days. I definitely have a tolerance, but I'm not sure I want to have one. I like the feeling this used to give me. Now it feels more like a gentle stimulation.
And yes, to answer, BananasAndOranges again, some people do take 4-FA pretty much for improved focus. 4-FA definitely provides me that, and for quite some time, too. All around, this is a great drug.
I have not done meth or high doses of some amphetamine, so maybe that's why I can appreciate something like 4-FA. Finally, I apparently do have a much higher sensitivity to stimulants, because everyone seems to be taking double the doses I do. I also gave 50 mg's to someone who never does stimulants (doesn't even drink coffee), and they barely felt anything at all.
Man, you're my kind of drug user. I realized a long time ago that chasing the 'ultimate high' is a worthless pursuit, because it is virtually impossible to attain, and maybe if you do, you will never attain it again. Enjoying the more simpler drugs and RoA is the way to go, imho.