I'd test it out on your runs and see what works. For me, I can normally stomach 2 gels (sis isotonic gels) an hour until 3 hrs and then I mix it up with whatever my stomach feels I can take in. Sometimes its banana's, crisps, flapjacks, peanuts... If my stomach starts to get a little tender - i'll drink some flat coke and that normally helps me a lot. I know a friend I've ran with that will literally take a picnic with her (cheese sandwiches, flapjacks etc).
I think the most important is not forcing your stomach if it does get tender but have plans in place if your current strategy doesn't work.
I'm a 5hr runner too so I know what you mean about being out there for a while!