Some items given as quest rewards vary in strength based on your level when you are given them. What is the minimum level I need to be to ensure that any of these items I receive are as strong as they can be?
In Oblivion it depended on the item. The level variations were part of the item's game data, so each item would have custom level breaks. It's a very useful feature for the designers to have, so we have every reason to believe it's the same in Skyrim.
Until we have access to the CK, or until someone extracts the item data with a custom tool, we won't be able to say with certainty what character level would trigger the highest tier of every levelled item in the game.