SGH- i would look into a shoe with a wider toe box, or seriously try going up another 1/2 size. You should not be losing that many toenails and blistering that badly in a marathon. The only time i kill toe nails is stubbing them on the trail, not from hitting the front of my shoe. Do you change your gait as you get farther into a marathon? Your feet may swell more than you think they do over that time. Maybe wear your regular shoes during training, but for 26 miles you need a half size LARGER?