A.P.
K., just a quick response to your relating going all night without needing to pump & going about 7-8 hours without breastfeeding. With breastmilk, it is demand creates supply. So as your body adjusted to your young daughter sleeping all night, it did not produce milk then. It creates the milk according to additional or decreased stimulation. Hence no engorgement or leaking. It was all gradual, not sudden.
So honestly, I question you pumping a lot the week before. There are so many variables in this... what is your training leading up to the event, what is your current breastfeeding schedule? If you increase pumping the week before, you will increase the amount of milk your body produces, hence the possibility of more engorgement on the day of the event.
One possibility is to add one time a day, beginning now, where you pump & freeze. A time that is relaxed & about 2 hours after & before feedings. Maybe a late night or early morning before or after she sleeps. Between now & May 10th, you'll build up a supply that you can use if you need it after the demanding day.
The physical exertion of the race day can affect your milk supply... It is one thing to exercise for an hour a day, another to vigorously exercise for 5-6. If it is a one time thing, likely you can recover & build up your supply post event. If it is ongoing, many events, it can affect your daily breastfeeding. One other thing to keep in mind, our body releases hormones that do filter through the breastmilk. So if you have had a demanding day, those "stress" hormones go right through. They may not affect the physical taste of the milk. They can affect her emotional state. Just food for thought.
Only you can decide what is best for you. Weigh your options, decide what is most important for you & your lovely daughter. The fact that you have breastfed exculsively for 5 months is awesome & great for your daughter. You will know if the timing is best now for the distance cycling, or, if, as a new mom you can wait a bit, cherish thiese precious moments with your daughter, & perhaps do the distance cycling once she has been weaned onto eating healthy foods.