I got three Macs with SD cards on: iMac 27 (in native slot); Macbook Pro Retina 15 (in native slot); Macbook Pro 15" 2008 (via Sonnet SDXC UHS-I Pro which I put to ExpressCard slot). All three cards are SDXC 128 GB and are always on. I use them to keep audio libraries for audio production software (ie. samples, patches, Reason refills) and some mp3 songs libraries. I don't remember now speed details, but when I tested with Black Magic, it was comparable to USB 2.0. Never had any problems with speed or durability.