Australis is such an improvement that I'm tempted to come back from Chrome. Everything feels very fluid and fast. I'd be curious to see the latest benchmarks on startup time, Javascript performance and such.
You're absolutely right that perception of speed is largely about experience. The animations are smooth, it doesn't jump around. But I can tell that the boot times are much faster now as well.
Both teams have done an excellent job. Seeing this release has encouraged me to finally donate to Mozilla. They do a lot of good for the web.