The server has the ability to send cars to you (their positions, as well as some other information) using different levels of detail. The different levels of detail require different numbers of bytes of information to be transmitted per car. Depending on the number of cars on track, the amount of space available in the "packet", and some other factors, the server will choose an appropriate mix of the level of detail it includes with each car it transmits to you. The higher your Connection Type selection, the more likely it is that the server will choose the higher detail level for more of the cars in the field.

The level of detail sent for any given car won't have any measurable impact on your CPU usage or your frame rate.

The extra overhead of handling the larger packets that can be generated when using the higher bandwidth selections might have a measurable increase in CPU usage IF there are enough cars in the session to actually use that extra space. See Max Cars below.