[dlo]

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."

[icebraining]

mnm1 said the breaks were for health reasons, whereas that seems focused on productivity.

[dlo]

Ah, right: "My peak concentration is usually right before break and after break it's generally gone."

One thing I do is, before I take a break, I dump my current notes, as well as things I'd like to do, into a Google Doc. When I return from my break, I take the time to read the notes, which loads pertinent facts back into working memory and gets me back into it.

Another practice that helps is that I let a fine-grained todo list guide me during work. I make sure to explicitly mark what I am currently working on. If I get distracted, it is straightforward to remind myself what I was doing, and once I am done with it, I know exactly what I should be doing next.