I have one of Autometer's "Ultimate" playback tachs. I forgot the # but it goes to 9,000 and does not have the driveshaft sensor. But it has been a VERY valuable tool in learning what is really going on as opposed to what you think you saw.

I have it rigged up to a button I press when I prestage to start the recording. It's next to the aux. fan switch I also turn off at that time just before the run.