I suggest before settling on a car, you create a full grid of AI, choose a track which shows the whole grid in one view, but doesn't use too much CPU (e.g. South City) and pause the game before anyone moves.
Then you can gauge the relative CPU usage in one of two ways.
1) With
unlimited frame rate get a reading of frame rate with the mod and compare that with another mod or official car.
2) Set a
fixed frame rate and check CPU usage for the draw. In Options - Misc click the car button then the P button and check CPU use for "Draw". A CPU test of this type must be done with a fixed, achievable frame rate so that the comparison can produce useful results.
If you find that a mod uses a lot of CPU to draw, here are some tips on how to reduce it, successfully applied to the N.400S GT4.
https://www.lfs.net/forum/post/2075561#post2075561