I think you should be able to balance whatever you get, regardless. The issue I see is total weight. If a 4S plane is designed w/ 3000mah in mind and you use 5000mah, that is a large percentage of the total weight. If you are talking about an 8S plane, the change in weight is a smaller percentage of the total flying weight of the plane.

Of course the plane needs to balance right, but you also want something that will fly well. Overloading with batteries means faster landings (or increased likelihood of stalls and 'pancake' landings), slower response, and more stress to the fuselage.

Not saying you can't find a plane that will work, but I would strongly suggest finding something where you can learn from others' experiences - if lots of people are flying a 4S plane on 5000's, then go for it. If none or only a few, be careful.