"The T3i can only AF in dim light down to -0.5EV. Same with T4i, T5i and T6i. The T7i now autofocuses down to -3EV, which is the same as the 6d, and now the 5D4."
Se o problema for desempenho em baixa luz no central, só T7i e 80D seriam um upgrade para você.