Should I install a Fast Ratio Steering Box?

Heck, I'd install it in a heartbeat. Better than letting it sit around, collecting dust. I don't know who told you about the understeer, but that sounds like B.S. to me. It's just less turns lock-to-lock and more of a ***** to park the car when you're cranking that wheel stopped.

Now, maybe an argument could be made that using it with skinny tires isn't an worthwhile use of that box.......but I'd still bolt it in right now!