Not sure I understand your question. Functional components and class components both use createClass internally IIRC. In any case, they are the same. A PureComponent is simply a Component with shouldComponentUpdate written for you. Functional components can't be pure, but you can use an enhancer for them.
I.e., do the gains from PureComponent exceed the cost of a Class? Personally I would assume they would otherwise no one would ever think of think using one, but it is an interesting question and set of metrics that could be gathered.