The MSFS 2020 Darkstar was outstanding at doing as you mentioned (getting from A to B in a super fast time - I do miss being able to go from USA to Asia, Australia, or Africa in just over an hour), but that was partly due to the limitation of MSFS 2020. The 275000 ft ceiling acted as a “de facto” autopilot for altitude, maintaining 275000 ft and it was mostly smooth, if you aimed for a proper trajectory, but you had to stay with it to gently steer it and made sure it did not start to descend or flip, but it was not hard at all. The Quasar, great as it is, does seem a bit sensitive and very easy to send into an uncontrollable spin. However, in most cases, it does eventually come out of it. I did crash once, when it took a nose dive, and literally anything I did could not get it to change course and stop the rapid nose dive. However, that only happened once.