Well, the drafting definitely helped for the first 60 miles of my Honolulu Century Bike ride today (something like 3400 people were in it!).
But after that, I was worn out. Most other people were too. Those groups who were not, just shot past the rest of us and we had no hope of trying to keep up. Meanwhile, when I came up on other riders, they were dragging even slower than I was so there was not much reason to draft them.
That was one hard ride for me. I think if I do it next year, I'll just start riding when I usually do - 3:00 AM or before - and let the other people eventually catch up to me. That would give me at least 3 hours 15 minutes more time riding before it gets hot - or windier.
I lose a lot of drafting that way, but for the first 10 miles especially, there were so many people, they slowed me down even just cruising.
Bob