What I meant was "We know there's tons of things we can still optimize, but we're just gonna release now anyways."
Again, that's just how software goes. I'm sure anyone who has released software could give you a laundry list of things he would have liked to have done, but didn't have time. Should they slide the release a year or two so they have time to feel better about how well it's optimized for speed? Generally, no.
At any rate, unless the software has been around for many decades and the best minds in computer science have failed to improve upon it, you can generally feel confident that there are tons of things you can still optimize.
Are you a programmer? The idea that there is a finish line for optimizing a program (beyond "This seems fast enough") is weird, and not the sort of thing I'd expect to hear from anyone who's ever done it. You do just have to stop at some point and release. Otherwise you'll keep improving things until the heat death of the universe.
IIRC, the Chrome team has a zero-tolerance policy on performance regressions. Since it auto-updates, it should get faster over time.