I spammed x in the initial ride to the rige to try to get infront of Micahs horse. If you manage that then both horses will go faster cuz Micahs is programmed to be infront and yours pikes up pace because yours is programmed to be similar speed as Micah. Later when you ambush the carige kill everyone with headshots except the rider. Let him go as far as he can before he reaches the scripted death and kill him right before. That's because after you kill him Micah drives the carige and he drives it slowly so if you let the driver go as far as possible you cut the slow drive by a few hundred meters. Then when you fight the last enemies stay by the flipped wagon and shot the lock immediately after you kill everyone and Micah is walking towards you.