The positive heritable mutations create proliferation of types, while the regression is an inhibitory function. Both are happening at once. Outliers do not always do well. The exceptionally stupid do stupid things and don't survive. The exceptionally brilliant have been, often, driven out of social populations, or burned as witches.

Without trying to blow smoke, I would start guessing at 110 and go up. Go hang out with some Mensa members and you'll see. I think Mensa entry is set at 132 for the Stanford–Binet , and 148 for the Cattell test. some of the lower end are not that apparently bright. If I were forced to bet, I'd say the Dunning-Kruger effect has fooled you into doubting yourself. You may want to test more to find out.