Finished the unova E4 last friday and...
Isn't that difficult, the level cap is 56 but i guarantee that if you reach it it will be more than enough to beat them all, the only thing i strongly recommend is buying healing items, ultra balls (for Zekrom) and not to make Unova your starting region because of the lack of a vs seeker to train there, other than that i didn't have much trouble, even the infamous Hydreigon that Ghetsis pushes around went down very quickly, once he took a boosted brick break to the face.
The cap wont give you troubles, i assure you. just plan your team.