I noticed top speed was easier to achieve at 75 PSI, however it felt more squirrelly going over loose gravel omni unclean roads. The sweet spot seems to be 60-65 PSI. The side walls recommend 50-100 which is such a wide range.
I used to always run 65psi with the stock slicks that came with the base Turbo as I thought that was the highest they could go. I've since put Marathon Plus HS440's on and, although they can take a higher psi of around 85, it still feels more comfortable to have them at around 60-65psi.