The problem strangely enough is the character models.. I loaded that same boarding event and switched on RT OSD. GPU never exceeded 10% CPU utilization is always high regardless of what the scene is, curiously it never actually maxed out. I then increased timescale and waited for corpses to despawn and gained a lot of frames. In fact, just looking at my fighters alone tanks the FPS from 120 to 55. Not normally a problem in other scenes. My guess is there is something in the deck scene that compounds what is already a very macabre issue.
What the hell is going on inside these character models? I can safely say its not a graphical constraint. Likely unnecessary but if you still need the save let me know how I can PM you the link. Couldn't see any option to PM on this site. Just don't have confidence that Google fully patched the privacy exploits in Googledrive links.