There are a lot of different perspectives on this. Everyone will have their own personal experience.
I went through a lot of iterations trying different things. It wasn't until I started to get the rest of my eating habits in line that I was able to get a better boost from any specific breakfast. Basically, I was eating too little protein through the day. When I finally balanced that out, I found that the standard big breakfast heavy on carbs gave me more of a boost on race day.
On Sunday, I ate a whole bagel with a *little* bit of butter. Then I had a full bowl of Kashi GoLean Crunch with Soymilk. About 2 hours before the race I had a Carnation Instant Breakfast. Then for the race I had 2 bottles. I drank half of the first one while warming up, then 1 whole bottle during the race.
Essentially, there are 168 hours in a week. If you ride 10 hours a week, that gives you 158 hours of week to get your eating habits in line. The more I dial in the *rest* of my life, the more I find that what I eat while riding/racing matters less and less. I think I could get through a race with only one bottle of water now and be fine.
As always though, YMMV. Here are threads
here and
here that may help as well.