Frame-sizing is a minefield. Even the traditional seat-tube length is fraught – it used to be centre-to-centre, but now is usually centre-to-top. However, a compact or semi-compact frame may well have a shorter seat-tube, though, on the other hand, it might be extended above the top-tube. Ultimately, a comfortable step-over top-tube height probably determines your maximum.
Then there's the length of the top-tube. This is often close to the seat-tube length, but not always. Actual fit can be modified by stem length or (less optimally) saddle position. Toe-overlap (if that worries you) can also be a factor, especially on smaller frames.
To answer the OP, I look for a 54cm top-tube, and a frame size (seat-tube length) around 54-56cm. I'm probably around 5'11" after allowing for shrinkage with age.