I am not sure I agree that it would necessarily be quicker. Evolutionarily speaking, a rat's brain's neurons switch just as fast as a humans. The number and density of neurons seem to define the level of cognition, not the switching speed.
I have a hunch that the constraint on switching speed actually results in intelligence rather than constrains it. Consider seizures in human brains for example.
Secondly, consider that humans have had the same brains for millennia and yet we still cannot improve them. We barely understand the first thing about them. I don't see how making the process faster, at the same level of cognition, would help.
And on top of that, if they have human intelligence, they'd be able to improve it in those few seconds (because we had and they'd have access to our research), make smarter AI, and on and on exponentially fast.