I just installed a 256 GB Samsung 840 Pro in my late 2007 15-inch MacBook Pro, and it is performing much slower than other people have experienced. In a Blackmagic Disk Speed Test, I get 127.6MB/135.2MB, but most people get well over 200MB/400MB. For instance, below are my results compared to someone else's with the same drive. Does anyone have any idea why it is so slow?
My results
Someone else's results
My results
Someone else's results