A common phototransistor could easily measure well over 100K pulses per second. If you go with an inductive pickup, I'd put a 47K resistor in line and a 5.1V zener diode (between resistor and arduino) as a shunt to ground to protect the arduino. You will find that the electrical supply in a car is the worst as far as spikes, sags and voltage dumps go. Prepare to harden your designs.