Lowest Audio latency achievable
This is entirely achievable.

OSX has been capable of sub-3ms latency for the past decade.

CoreAudio and CoreMIDI are built right into the OS for low-latency audio and MIDI support.

That being said, latency is a function of your entire system/signal chain. As you well know from your Windows experience, some tuning and configuration with respect to your specific audio hardware will be necessary to get the very best performance.

But even without tuning, OSX provides great latency performance out of the box. I've been using Logic and Live regularly since I switched to Mac about 7 years ago, and never had a complaint even in the early days when I just plugged things in and didn't tune any of the default settings.

As Apple users are wont to say, "It just works." But it works a little better if you spend some time optimizing the performance.