According to the calculator a VO2max of 30.4 is equivalent to a vVO2 of 6.67mph or a 9:00 pace. This means a desired goal of a 5:00 marathon pace (11:27) is 78.6% of your VO2max. Most marathon runners are somewhere between 60%-70% (for you 15:00 min/mile to 12:51 min/mile) but elite runners can take the percentage as high as 85%. So a 5:00 pace is beyond the upper end of normal for your current fitness level, although under really good conditions it may be possible. The calculator is heavily dependent on VO2max which for some people is not the best predictor of actual fitness paces (and previous race finishing times is better). In addition, if your VO2max is off it greatly impacts the calculator. If you had a VO2max of 35 you would be within your desired fitness level for desired pace.
Over the entirety of the marathon you will burn an estimated 3222.2 kcals. Given your pace is 78.6% VO2max, it is estimated that 2370.2 kcals of the 3222.2 total calories burned will come from glucose. Assuming an average female leg muscle mass of 15.3kg (21% of your body weight), you have 1221.8 calories of glucose stored in your leg muscles. This means without tapping into any other source you will have a deficit of 1148.4 calories of glucose. The average person can take an additional 100 kcals of glucose from the liver without putting the body in danger, thus your final deficit total is 1048.4 calories.
This means that either through a carb loading schedule prior to the race, or a nutrition plan during the race you need to consume an extra 1048.4 calories to complete the marathon without hitting the wall at the pace you desire (5:00 marathon) given your current fitness level. This breaks down to 209.7 calories per hour (or 52.4g of carbs per hour) if you decided to only use a nutrition plan during the race. To properly absorb 52.4 g of carbs per hour you would need to consume 26 ounces of water per hour. I would caution that if you haven't practiced taking in 52.4 g of carbs in training that your body might find it as a shock. You are another candidate for a good carb loading training plan as the best way for success with drinking gatorade at each of the aid stations as planned. For me, my favorite carb loading plan is to start it 4 days before the race, carb load for 3 days on complex carbs (for you totaling at least an extra 262 g carbs), and then the day before go back to my normal diet.
I would caution you to be careful with your pace in the beginning of the race. I've found by running by feel I have a better success rate, and in the end if I ignore my time and just enjoy the run it tends to go better. Research also shows that continuing to have positive thoughts during the race can improve your time significantly. The mind controls the body and lets it know whether at the current pace with the remaining mileage if it can maintain, but if the mind believes it can't then it starts to create the message of fatigue and that you need to slow down. My suggestion (and this is how I do it too) is to line up at your desired marathon finishing time (if they have pace marking spots at the beginning). At the start of the race, I let most of the people lined up around me to go past me. Mentally I feel like most people go out too fast, so if people with the same goal as me are passing me in the beginning then I know I must be going slow enough. Then half-way through the race I start to play Pac-Man and try to slowly catch each of those people who have passed me.
Best of Luck and let me know if you have any questions.
