If it were at all possible I'd give Bob a 4 day week, let him work on personal R&D stuff, or promote him to a level where he can use his competence to solve big

If it were at all possible I'd give Bob a 4 day week, let him work on personal R&D stuff, or promote him to a level where he can use his competence to solve bigger problems. If there are no more challenging problems to work on it's time for Bob to look for a new job as his career will be suffering.