Bob is having trouble with his download speeds. They just aren't consistent from computer to computer. Leo says it's important to understand that he's paying for *up to* the maximum download speed. It can vary wildly. But Bob says sometimes is slows down to a crawl on one of his computers. Leo says he can experiment by rebooting the computer and see if it goes back up to max download speeds. If so, that means there's a program running. That's called a "memory leak" and the computer is using up bandwidth by that program.
Buffer bloat with his router could be the issue as well. Bob should try another speed test. TestMy.Net, Seriousbit.com, DSLReports.com has a great speed test, and a great article on what buffer bloat is and how to fix it. A better router would probably solve the issue.