I have a 6 qt kitchen aid, and was making 4 loaves. My machine really struggled too ( never did with old formula). I tried dividing the dough when my machine overheated several times, but it still struggled and overheated. If the oatmeal mixture were added during the main mixing time rather than adding at the end do you think that that would loosen the dough enough that the mixer would handle it better?
Otherwise the enddought was very nice and loaves looked good.