MacBook Pro 15" has two 6G SATA Ports that are Reliable and Fast
OWC informed me a few weeks ago that the June 2012 MacBook Pro 15" (non-Retina) has dual 6G ports that are both reliable for use with 6G SATA SSDs, unlike the prior model, which was hit and miss.
I’ve had the 15" 2.7 GHz MacBook Pro in hand, and indeed it supports consistent 6G performance, using the OWC Data Doubler to install a 2nd 6G drive into the optical bay.
Test results from the June 2012 15" Macbook Pro.