Vastly Inconsistent Bandwidths Across Multiple Windows 7 Machines

I recently started a subscription with Comcast for a 50mb Down/10 mb Up high speed internet service.I am using 3 different websites to analyze the download speed of this connection on multiple computers (speedtest.comcast.net, speedtest.net, speakeasy.net/speedtest).The issue is, the 50mb download speed works for some of my machines but not for others.The following machines receive the full 50mb (or higher) download speeds when checking with the above sites: [code] When I try this with my other Windows 7 machines, I get results of less than 10mb down. These machines are: [code] These tests were conducted with direct hard line hookup to the modem, no router.I know for a fact that the service is working at full capacity, since I get the full download/upload speeds with the 3 machines. But I cannot figure out why the other two are more than 80% slower.All of the firewall settings are identical across the Windows 7 machines. I tried starting my my ASUS machine in safemode, to see if some particular process was slowing things down, but the slower internet speeds remained.I was hoping that someone might have some idea what is causing this, or maybe some idea of what to compare between the two machines. While I am fairly computer-savvy, I don't know a lot about networking.