I am trying to download El Capitan from the App Store, it's going so slow it's saying it's going to take days to complete. My connection is fine, during tests I was getting 7MB/sec, however, this download has taken the best part of a day to download 600MB. I need this to restore a Macbook back to factory for a sale, the guy was supposed to be collecting today and i've had to delay it. Is there any way I can speed this up?  I downloaded a torrent and it said it couldn't verify it or had been tampered with.