After quite a bit of research, I've settled on Hammer Nutrition as my primary solution. Lately, I've used HEED powder on training runs to keep the electrolytes up without a lot of sugar. I've not made my way through all of the flavors, but Subtle Melon really works well for me - even in a double strength bottle. The 'subtle' in the name certainly rings true and makes for easy intake.
For fuel, I'm focusing on Hammer Gel - vanilla flavor as the primary solution. I started with single-use gel packs, but have moved on to a 650ml bottle that I can put into smaller distribution flasks. Wearing a few flasks on my running belt, while carrying a HEED-spiked water bottle with a carrying strap gives me what I need for two to three hour workouts.
My next experiment will be with protein. Based on my reading, for endurance events, such as 40for40, I'm going to need to integrate protein into my carbohydrate intake. Hammer Nutrition has an interesting mix called Perpetuem that functions both as a carbohydrate replenishment solution and a protein source. There is even a flavor - Caffe Latte - that incorporates a mild dose of caffeine into the mix.
For days when I really get behind and I start to flag, I carry Sports Beans - lemon-lime or orange flavor. These are made with cane sugars so it doesn't meet a low-sugar criteria, but I find that I get quicker relief in the event that I'm starting to hit the wall on a long training run.
All in all, I plan to go to Phoenix with the following strategy. HEED prior to the race and possibly a few ounces to carry me through the first five kilometers. From there forward, I'll rely on good old water at the water stations for hydration. Hammer Gel will be my first choice for fuel, carried in distribution flasks on my race belt. After 20 kilometers, I'm going to mix in some Perpetuem, using the solid tabs. I'll have some Sports Beans in reserve in the case that things get tough. Nothing like a sugar rush to bring morale back.
After the marathon, I'll be able to hone my intake plan prior to making the big run in April. Stay tuned for a post-Phoenix update for what worked and what didn't.