To check the FPS, us CTRL-F.

For the rest of the answer, thanks to Dave Henrie:

"Here is something you can do to help your fps. This involves editing your .plr file. So make sure you backup the file before you begin to edit.
open your .plr file with a text editor and look for this line in the [graphic options] section
Load Opponent Cockpits="0" // Whether to load gauges and LCD for opponents, don't turn off if you're planning on hot-swapping vehicles in multiplayer
Make this = to zero. Since we don't swap cars or drivers, you don't need those cockpits loaded.
next further down in the same section:
Max Visible Vehicles="10"
Extra Visible Vehicles="10" // Extra vehicles shown in non-driving situations
These default to a pretty high number, especially the 2nd one. something like 104 vehicles. That is just WAY to much stuff to worry about.
Finally near the bottom of the [graphic options] section is another few lines you can change;
Display Icons="2" // Icons displayed if HUD is off: 0 = none, 1 = flags only, 2 = all
I changed this to =2 so that all the icons show up all the time. This one is very valuable in the pits or when you get a black flag.
Max Headlights="4" // Max headlights visible relative to your car.
again, making this change reduces realism slightly but reduces the load on your system.
Next go into the main menu and choose the options section of the multiplayer screen. There you can choose the speed of your connection. Reduce it as much as possible. I have a 5mbs cable line but I choose either DSL or ISDN. The server will attempt to send you as much information as you can accept. But doing so will bog down other cars. So go online with the servers during the practice weeks and see how low you can adjust the connection speed without the track getting jerky when you corner. If you see that, you've set it too low.
Also from the main menu, you can choose to change your display options. Go to display\options and reduce the number of visible cars. This isn't like Nascar at Daytona where you can see all the cars going around a corner. You only need to be aware of the cars closest to you on-track.
Your 3d config probably can match your desktop screen size and refresh rate, but you might want to try reducing the screen size slightly and lowering the refresh rate. Previous ISI sims would run the 3d config utility and then display a polygon rate. This was a good way to judge how well your card performed. rF has a texture bar on the upper left when you activate the fps counter. THis should be GREEN. If you have a yellow texture bar, then you are stressing your system. Reduce screen resolution until you have at least a partial bar that is all green."