This is what Elon says verbatim:
"Hardware 3 will not be as good as Hardware 4, but I’m confident that Hardware 3 will so far exceed the safety of the average human. So how do we get ultimately to – let’s say, for argument’s sake, if Hardware 3 can be, say, 200% or 300% safer than humans, Hardware 4 might be 500% or 600%. It will be Hardware 5 beyond that. But what really matters is are we improving the average safety on the road."
Elon Musk kills hope of Tesla retrofitting new Autopilot/Self-Driving hardware
Note how he does not refer to L5 or any levels at all. Plus, Elon's definition of L5 may not necessarily match your definition or the industry's definition in the first place. I've noted his definitions do not match with how some may interpret it: for example when he says "feature complete self driving" he actually means door-to door SAE L2.
Autonomous Car Progress
Even for industry definitions, it can have a huge leeway for performance. See the various L4 companies and how different they perform. Compare for example the two most prominent: Cruise vs Waymo. Cruise has had many incidents where the car would halt in the middle of traffic (even in the middle of intersections) needing a person to come rescue it. Waymo have had much less.