I'm not sure speed alone, by itself, is a solution. If you speed down a game by, say, 70% there would probably be no difference than if you sped it down by 90%, since there's a limit to what the character can do in a given second. Mario, for instance, once you jump, there's not much to do until he actually lands.
Suppose the same would happen if we had the capability to speed down time in our actual lives. Sure you could dodge bullets and win F1 races from time to time, but the actual day-to-day tasks, that take the majority of our time wouldn't be improved much. If you need to eat lunch, eating it in an optimal way won't give you much advantage in comparison to regular people that don't take the fork to their mouths following a perfect parabola.
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.
From Toby Ord:
Though there are limits to what AIs could do with sheer speed, it's interesting that great performance can be achieved with speed alone, that this allows different strategies from usual ones, and that it allows the exploitation of otherwise unexploitable glitches and bugs in the setup.