Circuit size for "at least n inputs are true"
From S. Chaudhuri, J. Radhakrishnan. Deterministic Restrictions in Circuit Complexity:

Theorem 6.1: A circuit computing $T_k^n$ with $k \leq n^{1/3}$ has $\Omega(k^2(\ln n)/\ln k)$ gates

Where $T_k^n$ is the boolean function that has the value 1 iff at least $k$ of its inputs have the value 1 (threshold function).