I discovered a nifty trick for those excruciatingly slow Apple Update downloads. My friend left his broken 2008 Mac Pro with me last week. It turned out that he just neglected to plug in the display power supply. The computer has been down for a year(!) because of that.
Since the machine hadn't run since last summer, he was still using Yosemite so I decided to do his free upgrade to El Capitan because obviously that was going to be over his head too.