One thing to remember is that German tanks generally outclassed the western Allies tanks by the time of D-day. The M4 would lose going one on one with almost an

One thing to remember is that German tanks generally outclassed the western Allies tanks by the time of D-day. The M4 would lose going one on one with almost any of the main line German tanks, unless it had very favorable terrain. The number of Panthers that Germany could field in the west was very much important to the success of the D-day invasions. Had the allies had solid intelligence that Germany had several times greater number Panthers and Tigers, it's entirely possible that they would have done D-day completely differently. Of course, this is all with hindsight.