From the perspective of us looking directly down on a parallel “plate” of a galaxy (with the other galaxy viewing us in the same way), relative differences in speed for the situation of same direction of rotation will be much smaller than for opposite directions.
But between any point in one galaxy to another, just as much matter will be moving closer as moving away. Regardless of same or opposite rotations.
But perhaps greater red shift and greater blue shift (as apposed to lesser of both) as a practical matter of telescopes vs. their cross spectrum sensitivities, means more light detected.
But between any point in one galaxy to another, just as much matter will be moving closer as moving away. Regardless of same or opposite rotations.
But perhaps greater red shift and greater blue shift (as apposed to lesser of both) as a practical matter of telescopes vs. their cross spectrum sensitivities, means more light detected.