Nutrition on the Run

I'm a fairly experienced marathoner and have my nutrition nailed down for a stand alone race. In average weather conditions, I'll take a Hammer Gel every 4.5 miles and drink only water. I may or may not take the 5th gel, depending on how my race is going. I alternate caffeinated with non-caffeinated options.

I'm dialing in my nutrition on the bike as I train for my first Ironman (Lake Placed on July 28th). I'm taking in a mixture of Perpetuem (400 cal per bottle that will last anywhere from 60-90 minutes), Hammer Gels, and the occasional Snickers (that I'll have in my special needs bag should I feel like one). My pre-ride breakfasts usually total around 800 cal. I feel well nourished on the bike and have completed multiple rides in the 80-95 mile range. This Saturday, I'll ride around 105-110 and do not anticipate any concerns given how well my nutrition is going.

But for the race ... should I plan my run nutrition any differently? My current plan is to carry a handheld with 5 Hammer Gels. I'll refill the handheld (water) with water as it drains and drink according to my normal routine for a marathon. I've used S-Caps in the past on particularly hot days and feel comfortable with working them into the mix if I need to.

Is this a short-sighted run plan? That's only 450 calories for the run. It's what I normally do for a marathon, but I'll be more depleted at the start than what is typical. I don't want to run with Perpetuem ... Hammer Gels are about all I've can tolerate without developing GI issues while running. I've only done one brick run following a long ride (6 miles) and felt fine. I completed a 17 miler this past Sunday with only one gel and can usually go for as long as 15 without any water or nutrition (unless it's hot/humid).

Any thoughts will be greatly appreciated. I'll be around 185 (6'2") on race day. 46 years old if that matters.