I had Logic’s Process Buffer Range set to medium.
Running great here on a Mac Pro 8-core, 24GB RAM, OSX Mavericks. In my own extensive testing against Windows 7, Cubase tends to perform better at very low latencies on Windows (of similar hardware), but performance of C7.5 on OSX is still very good and can handle highly complex projects without problems. At higher latencies, the gap closes. for me, it’s not an issue, and I’m quite happy running Cubase on a Mac. If you need to get into massive-count orchestral templates you may run into issues, in which case you’ll probably end up using VE Pro to help out any way.
Equip your machine with some SSD drives and use an audio interface with excellent drivers from a high-quality developer like RME, and you’ll get some superb performance. And when you run out of CPU resources, again, you can use VE Pro and slave an external machine. Good luck!