The golden age of six stars
Back in the days of San Andreas and GTA 4, hitting six stars felt like an achievement. You were basically fighting a war. The military would roll into town with Rhino tanks, helicopters would rain fire on you, and the streets would lock down under martial law. GTA 5 dialed that way back, capping out at SWAT teams and FIB agents even when you were causing maximum destruction.
What to expect at the highest level
Whether they call it five stars or six stars, surviving the max level in GTA 6 is going to be a nightmare in the best way possible. The police AI is getting a massive overhaul.
Instead of just blindly ramming your car, the tactical teams are going to use real strategies. We are expecting them to use tear gas and flashbangs to flush you out of buildings. They will probably deploy heavy drones to track you through the swamps where helicopters can't easily follow.
Will the military actually show up?
Given how crazy Florida gets in real life, it would make total sense for the in game equivalent of the National Guard to get called in if you cause enough damage in Vice City. I am really hoping we see armored transports and military grade hardware rolling down the neon streets again.
Because the AI is so much smarter now, you won't be able to just hop in a fast car and outrun them on the highway. You will really need to use the new stealth mechanics, duck into the subway tunnels, or rely on safehouses if you want to survive the absolute worst they can throw at you.