How FixedUpdate should be handle using Job ?

Im not really sure if this should be in this forum section, but it's more like, how other people do it. So i have a problem regarding FixedUpdate and the Job System, each Update, i calculate some vector position and apply it, its a step system, so i need something like FixedUpdate that i can trust, the problem with FixedUpdate is that it get called many time if the framerate is low, resulting in a snowball effect of job and cpu ms, i can probably reduce that ms by disposing the array and stuff after the FixedUpdate, but im wondering how i should handle this situation in order to have a reliable system and still have good performance ?
For example, i can handle 10.000 transforms inside update for 9ms when FixedUpdate is at 300ms
In the other hand i can handle 5000 transforms inside update for 4.5ms when FixedUpdate is at 2ms
It make sense but it's also really sad to see that when you are looking for performance