Thinking aloud:
45 techs in long game means less than 40 in normal, well played non-dom game. So let's say you get three free techs from FI special ability.
Spying. In Civ 5 diety you could get 5-6 free techs from spying. A 25% boost would be equal to at most 1.5 free techs.
I'm making an assumption that Spying is fairly equal to BNW - it's obviously not:
a)It seems like you get less spies in BE, even if you get as many as you can, but you can beeline them to get them earlier.
b)Spies can do other things. Those "other things" may be more powerful, especially from a domination point of view, in BE than BNW.
But just for science, it appears that FI would be better than ARC. This is different than what I originally thought; that ARC would be very powerful on higher levels. What do y'all think?