ok, so ive ran 4 marathons and everytime when I am on pace for 3:07-10 i slow down the last few miles and one time got such bad leg crams that had to stop and walk it off bc my muscles wouldnt contract. so, this time i plan on running long runs everyweek of 14-18 miles. in the past when training Ive only hit something lame like 13 and thats probably the main reason that i hurt at the end. i think my medium runs 8-9 miles are around 6:55-7, so is it bad if i run long runs close to 8 min pace if i want to run the marathon around 310???