(Really I am procrastinating, I need to get outside for a sea swim momentarily!)
Hard to predict Ironman paces - too many factors. The most obvious big one is weather - my bike time won't be affected hugely by warm versus cool weather (though it will be slowed if there's heavy rain due to caution on descents), but it potentially makes a huge difference to run pace.
Running the numbers just now, I'm thinking along these lines.
It's a long transition in Wisconsin, at least 10 minutes for each, maybe longer.
Swim will probably come in around 1:45. I am a fairly consistent swimmer and take a very easy pace on the longer swims; the goal is to come out of the water as fresh as possible. Say 1:40-1:50 anyway. Will hope for some good stretches of drafting.
Bike pace is very difficult to predict. Minimum pace of 14.0mph would yield a bike split of 7:59; realistic maximum pace of 15.6mph yields 7:10. If I have a sub-7:00 split I have ridden too fast and will pay for it on the run! Will use a HR cap for pacing (135-38, mid-zone 2 - 135 for first half, 138 for second), but hills inevitably bump up HR.
Run pace is temperature-dependent and also related to whether or not I have used good judgment on the bike. I am pretty sure I can hold minimum 14:00/mi. pace as a mix of jogging and walking, which would give a run split of 6:06:48 (assuming you make the bike cutoffs, you still have 6:30 to finish the marathon, and I think that I am in good nick as far as making cutoffs goes). If I am having a great day and the weather permits, I would be looking at a top speed of 12:30/mi. (It is very different from running an open marathon - marathon PR is 4:16, and really I should be able to go quite a bit faster than that if I train towards that end, as I was much hampered by undiagnosed asthma - I'm hoping to run a sub-4:00 marathon sometime in the next few years.) That would give a split of 5:27.
Adding in transitions, the absolute best-case scenario is then something like 14:45, with a more realistic finishing time of 16:00-16:20. 17:00 is the official cutoff, and I think I should be able to make it. Now I am just superstitiously hoping that nothing bad happens in the way of illness, injury or other calamity in the intervening weeks!