One of the things that was mentioned at the BSS evening was to just 'go race your bike.' Since I only just race my bike a few times a year...once on the road this year, several on the dirt, I'm going to apply this to triathlon.
How many times have you looked at the start list to see who is racing? I confess, I do that. How many times do you already have the outcome figured out in your head before the race? I confess, that I do NOT do. By that I mean that you know who's going to out swim you, who you are going to ride with, and who you have to out run. Maybe it's not quite like that, but it might be close.
So, there comes a time when the best thing to do is just line up and race. Forget all the BS that is out there. Forget the hard workout that you did on the Friday before. Forget the heart rate monitor. Forget the powermeter...well, don't forget it, just don't look at it. Everyone is beatable. Everyone can have a bad day or they can have a breakthrough day. YOU could have a breakthrough day. Just wake up, eat your breakfast, and then go race.
So, instead of worrying about who is there, how fit they are, what bike they are riding, what they ate for breakfast, what 'zone' you should be in for each race leg, and just worry about you and what you are there to do. In my case that's generally to just go swim hard, bike hard, and run hard.
Disclaimer: I don't know if I would just race an Ironman. I would probably suggest looking at the HR monitor or powermeter for that one.