After a good deal of testing, I've come up with the following classes:
900hp will be for the fastest cars, those that can reach speeds in excess of 240mph on their own without drafting.
750hp will be the next one down the line. Cars which can reach nearly 230mph on their own. I take it this will be the most popular class, as this is where most of the 600pp cars will fall under.
600hp is where most of the 550pp cars will be participating as well as others with average top speeds just under 220mph.
400hp-FF. This speaks for itself. 400 horsepower, Front-engine, front-wheel-drive cars will duke it out in this class.
If anyone wants to share their thoughts or input, feel free to reply to the thread. Until the season starts, these numbers aren't final. Any input is appreciated.