Fast in reverse.

Depends, how many miles on the engine? Wear and tear and rob an engine of some power. You might also have wear on the torque converter and clutches and some slipping. There's no reason to be doing more than 20 in reverse anyhow, unless your driving on a stunt course. Your suspension is built to handle bumps moving forward, very easy to break things going that speed in reverse. Keep in mind, most reverse gears are higher than even the 1st forward gear. So it's not going to get up to any great speed at max engine RPM. You have a limiter on your engine (likely 3K RPMs) If you have your transmission gear info you can calculate a potential speed, Engine RPM/ratio = RPM at the wheel. You might have a tag on the door or jamb that gives all tranny gear ratios, or at least tranny type, you can look up online what ratios it has. I'm guessing somewhere around 2.26:1, which is actually better than most cars as far as a reverse gear goes.