With regard to floors, afaik even DOOM didn't do them correctly. With vertical walls, the perspective divide needs to be done only once per column of pixels for a given wall segment.

For floors, unfortunately there's no such luxury, and if I remember correctly DOOM subdivided floors into patches, and only did proper perspective at the corners, and interpolated inbetween.

For floors the perspective divide is once per row, just like for walls it's once per column.

The BSP may have led to some floor subdivisions, especially as it needs convex sectors. I don't remember if the engine would coalesce adjacent floor spans into a single one, but I hope it did.