Well, Steam is one big hunk of crap on my machines, actually I don't think it works, not compatible. Plus someone is hacking my account all around the world, I keep getting emails.
A Sata 3 Drive like he has, should NOT be capped at 10MB/s, that's why I think it might be a driver issue, or there is a bottleneck on his Motherboard somewhere. I always go back to Video Drivers, because when not installed right it causes the same kind of problem.
Is there some Video setting, that makes a Video Cache file on the main hard drive? This is why I use cheap Video cards, I don't play games, so I don't need all that power. Whether is is a Video Card Driver issue here or a SATA 3 Data bus issue, something is not right and he's getting slower than ATA speeds.