Got my new iMac 27" a couple days back. Did a couple of speed tests and found that the mechanical drive read/write speed is roughly 115MB/sec, and the SSD is around 185MB/sec read. After having certain apps on both hard drives and launching them from both fresh boots and normal usage, there seems to be little difference in load times or in real world use. It's all the more noticeable after coming from a mercury extreme pro OWC drive of course, but from the stock apple drives, I'm questioning wether or not returning it and just bumping to a 2TB drive and saving a few hundred £££ due to so little performance gains. Obviously the downsides are the the time it takes to spin up after the Mac has been asleep, but even with an SSD present the OS still has to wait for the mechanical drive to spin up, so its negligable.