If the tests are, in part, for your own understanding, hitting a ceiling will not likely give you a full understanding of his abilities.
If we had simply kept having DD take lower-ceiling and grade level tests, we really would still have had a limited understanding of her abilities. When she finally took an out-of-level test, followed by a test with a higher ceiling, we had a much better understanding of her abilities and potential. In part, it depends on what you are hoping to get out of the testing.
