I have 1GHz computer and when i play without oponents FPS is about 40, when see few opponents FPS falls dramatically.
Maybe such option would be helpful: SIMPLE CARS OPONENTS ? What do you think ?

Just turn User Lod to minimum and you will have 10 fps more.

This is already in. Only the closest cars have the full physics simulation and there is an option to lessen the graphics of far away cars too.