[jeroenhd]

On many laptops you can disable boosting speeds and lock down the frequency (thermals permitting). I don't know if Apple's devices allow for such measures, but close-to-constant performance without fan noise can be a matter of configuration.

You can try running these chips at their boost clock all the time by attaching coolers, but the hardware wasn't designed for that and neither was the software. It's easier (and more power efficient) to clock down if you care about maintaining a set speed. With a battery capacity designed for short bursts, you'll also lose out on battery life if you decide to crank the hardware.

The Macbook Air and its competition (MS Surface etc.) are completely silent because they are fanless, and I don't expect their performance to be inadequate for anything but the most CPU intensive tasks. The Airjet will add some airflow, so while the difference may be minjmal, it'll always end up louder than before.