I peaked as a USCF A player. Obviously im just speaking for myself, but i generally looked at my candidate moves, 2 maybe 3 moves ahead. "What would i do, what would my opponent do, what would i do, what would my opponent do?"
Obviously, forced lines can be calculated deeper.
I would appreciate it if anybody rated 1800-2200 FIDE or USCF would tell me how deep they can accurately calculate in a classical game. Also please specify whether your answer is full moves or ply.