You might enjoy reading the section, "Intensely Single-Task," in this article, Philip Guo's "How to Be Effective."

http://pgbovine.net/productivity-tips.htm

He also expanded that section into a full article:

http://www.pgbovine.net/intense-single-tasking.htm

Here is an excerpt I think you might find useful: "This tip has had the greatest benefit to my effectiveness: When you want to work on a task (e.g., from your to-do list), get your mind to enter a specific 'mode' where it only knows how to do that task. Forget everything else. Remain fixed in that mode until you get tired and have to "break character". Then move onto the next task and repeat."

I think it addresses: "Tasks take way longer to complete with forced breaks, especially if the breaks are longer."