So it's time to think over your goals for the Shamrock Sportsfest and what that means for your pace, so if you have set a personal goal, can you reach that goal by running or do you need to add some walking? This may be an analytical approach but work out what average pace you will need. If you can achieve this average through a run/walk plan then try building in specific walk blocks earlier in the race for example walking for 2 or 3 minutes through each drink stop and then plan to start running again after 2 or 3 minutes. Another strategy during your training is to make sure you are not going out too hard for those first 10 miles as this unduly fatigues you. Make sure you are taking on calories through sports drinks or water/gels, this keeps your energy levels up and will help prevent fatigue. During your training also try pushing those limits back a little each time you run, go that little distance further each time and say "I told you so, see I can do it!" to that negative voice and when you do, smile to yourself or for the world to see. :))