The above is true, but bare in mind you can't always get a faster fan down to as low RPM as a slower one. Starting voltages and minimum PWM speeds apply, so it's not just as simple as fan controlling a faster fan. You still need to work out what your main priority is.
To get a 120mm to be truly silent they often need to be down to ~600RPM, and the question is would the 2000RPM fan get/start that low? Many won't. That said, if you aren't that bothered about silent computing then the 2000RPM might be fine for you.