Blackman-Tukey periodogram?
The resolution of the Blackman-Tukey periodogram estimator is $\mathcal{O}(1/M)$, whereas its variance is on the $\mathcal{O}(M/N)$. This compromise between resolution and variance is to be considered when choosing the window’s length.

I have paraphrased Peter Stoica's beautiful explanation from here (check Section 2.5)