The joystick puts out a value from -1 to 1 on each axis.
It is easy enough to see in the game that for any particular cl_forrwardspeed setting that a higher sensitivity results in faster motion or greater response to a particular joystick input. If the sensitivity was used as a divisor then a higher sensitivity setting would result in less forward speed or response to a given joystick input.
In the code the joystick input is multiplied by the sensitivity setting. This means that the the sensitivity is a linear as opposed to a non-linear acceleration curve. I am in the process of trying to create a non-linear sensitivity response.
It would be helpful if the game had a current forward speed display like the fps one. Hmm...
Maybe, I could hack the FPS display to reflect current forward speed. That would be interesting.