Actually I kind of screwd up my last mesage. Since you increased DELTA_SEGMENTS_PER_SECOND I assumed you want higher precision and I predicated the first part of the message with for constant delta segmentation error. But I did it only in my head. With this predicate valid point 1 and point 2 are the same.
If you lower feedrate and want to keep constant error, then you should lower DELTA_SEGMENTS_PER_SECOND too.
If you decrease DELTA_SEGMENTS_PER_SECOND, then you should lower maximum feedrate to keep the same delta segmentation error. So point one and point two must be done together to lower CPU load (and not to make errors worse).
If you lower feedrate and want to keep constant error, then you should lower DELTA_SEGMENTS_PER_SECOND too.
If you decrease DELTA_SEGMENTS_PER_SECOND, then you should lower maximum feedrate to keep the same delta segmentation error. So point one and point two must be done together to lower CPU load (and not to make errors worse).