The only thing to keep in mind if you use a gear at a lower RPM is that your duty cycle is going to be much higher than you'll get with your real pickup at it's true RPM, issues like your (unintentional) debounce circuit eating your pulses aren't going to be apparent necessarily with that kind of simulation. It will be good for all the other non-EMI stuff.
When I was first building my tach sense circuit I just used a regular soundcard outputting a square wave to do my bench tests on, just run it through a transistor to boost up to the voltages you're sensing. It makes it very easy to get dead accurate timing reference with no moving parts.