Group delay in low frequencies
Just as a reminder, group-delay due to the loudspeaker in a box is limited to about 0.15 * alignement order / frequency, which is also equivalent to (0.15 * order) periods.
Ie for a standard 4th order bass-reflex with a standard B4 at 30Hz, max group-delay is about 20ms.
So if you measure group delay of 60, 70ms or more, this is due to the room modes not to the loudspeaker itself !
Considering that a group-delay of 1 period (1 cycle) is non audible in low frequencies, we can consider that both 4th or 6th orders alignement should not be audible in any case.