I think it is reasonable to say that the question of whether to change fan ratios is one that remains unresolved in the Pelican community. Should a street engine be overdriven? Should a race engine be underdriven? Or vice versa?
In order to better understand the issues involved, I did a few calculations in Excel. For many years here, there's been concern about whether the tips of the fan blades go past the speed of sound. I think the reason people are concerned about this is because in the aviation world, fast-turning 88" seaplane props experience the tips going sonic, resulting in a tremendous noise and potentially harmful vibration.
But it turns out that even the most overdriven, largest diameter fans don't go anywhere near the sonic limit. As the below graph shows, the popular combinations of ratio and fan diameter are well below sonic, and even combinations that never originally came from the factory, e.g. a 250mm fan with a 1.8 drive ratio, are still comfortably below the limit.
(Interestingly enough, an 88" seaplane prop at 3000 RPM runs at 102% Mach. No WONDER they are so noisy)