Standardized IQ tests have specific times for completion for a reason. With more time (and the conscientiousness to actually use it) everyone would do better at them. So a speed increase is an IQ increase.

I think of my mental processing as a kind of information metabolism, with an equivalent of hunger: boredom. So I expect a smarter/faster thinker would need more input to process, much like a more muscular body needs more food. That, at the very least, should cause a smarter/faster thinker to interact with its environment substantially different from a standard rate one.