Ahriman
Tyrant
Basically here are the cautions noticed so far:
1. Anything exponential goes crazy with very large cities. This also applies to even quadratics like n^2 if not very careful about small constants. (Even then, 90^2= 8100 points and unless you're dividing by a large constant that's out of control, and if you need to divide by say 100 than this component isn't significant as it only produces 4 science at size 20, so most of the early science will still be in the linear component).
2. Anything with a negative constant can makes early rush strategies, particularly warrior rush too strong.
I'd emphasize both of these cautions.
I think the right way to reduce ICS is with happiness per city, food requirements for larger pop (one of the suggestions I had before was to split the hopsital in half, leaving half its effect in place and making the other half available from an aqueduct building at engineering) and city-boosters.
1 science per pop is nice and simple, messing with this isn't the right approach I think.