I have installed an Extreme SSD in my MacBook Pro mid 2012 (which is SATA III). Everything updated, firmware (211), OSX (Yosemite 10.10.2), all of it (SMC and EFI).
My negotiated speed is only 1.5 Gb and a lot of spinning rainbow circles (the annoying beach balls).
I've tried using R211m in order to get at least 3 Gb/s but doesn't work.
Anybody can give me a hand? It's driving me crazy spend a considerable ammount of money to have a SATA i disk instead of my (hopefully bought) SATA iii disc.
My chipset is Intel, so nothing to do with the NVidia uncompatibilities.
Thank you all in advance!