Fiesta island

Marathon training today with Matt. We drove to Fiesta Island which is in the middle of Mission Bay Park, next to SeaWorld. Matt started running and slowly disappeared in the distance. I expected him to pass me at least a couple of time on our circuit. I guess I did pretty good since he never did. I walked the 17.6 miles in 3h20mn (4 times around the island). This was my longest walk so far and the best pace yet; 5.28mph. First time around was the warm-up and I felt great doing rounds 2 and 3. Doing round 4 took some will power though; I really felt it in my legs. The marathon is 26.2 miles so I would still have about 2 more hours at that pace. Now I am not so certain. The next long walk is 20 miles; about 4 hours. I know that I have to slow the pace a little bit if I want to keep the momentum and not fall apart.