The Saffir-Simpson scale was created in 1971, and at that time the highest category hurricane was 5 (the scale is 1 to 5) with sustained winds of greater than 157 mph. Hurricane Dorian had sustained winds of 185 mph. If you follow the same progression of the scale, then Category 6 would be sustained winds of 183 or higher and
Dorian would be a Category 6. But of course the scale doesn't go that high since the creators of the scale did not anticipate a storm of such intensity.
This is different. The Bahamas has not been hit with a Category 6 hurricane before. Thousands of people have already evacuated Grand Bahama and Abaco, and thousands more are lined up desperately waiting to leave because their homes and livelihoods have been destroyed. This has never happened before, despite the fact that hurricanes have been hitting the Bahamas for centuries. I call this new ground.