If you're driving 45 in a 40, that may sound like 12% faster, but once you add traffic, lights, stop signs, turns, etc - you'll find that the 12% all but evaporates. Even if you're really pushing it and going 15 over, at most speeds and for most typical commutes, it saves very little.
Most of the time speeding ends up saving on the order of seconds on ~30 minutes or shorter trips.
Just about the only time it can be noticeable is if you're really pushing it (going to get pulled over speeds) on a nearly empty highway for a commute of 1.5+ hours.
This overconfidence causes humans to take unnecessary risks that not only endanger themselves, but everyone else on the road.
After taking several dozen Waymo rides and watching them negotiate complex and ambiguous driving scenarios, including many situations where overconfident drivers are driving dangerously, I realize that Waymo is a far better driver than I am.
Waymos don't just prevent a large percentage of accidents by making fewer mistakes than a human driver, but Waymos also avoid a lot of accidents caused by other distracted and careless human drivers.
Now when I have to drive a car myself, my goal is to try to drive as much like a Waymo as I can.
You have the group that's really bad and does things like drive drunk, weave in and out of traffic, do their makeup and so on.
The other group generally pays attention and tries to drive safely. This is larger than the first group and realistically there's not all that much difference within the group.
If you're in group two you will think you're above average because the comparison is to the crap drivers in group one.