The thing that REALLY improved my endurance was doing full 5-section PT's. Since I had some money to spare, I bought pre-arranged 5-section PT's from Cambridge for about $9-10 apiece. They put in a section from an older PT into the selected 4-section PT.
@DumbHollywoodActor Read Pacifico's comment. It can be assumed that 7Sage's license just happened to be up for renewal before Cambridge. I have a feeling it won't be long before Cambridge will have to change their policy as well.
Now that you're done with the curriculum, I think you'd benefit most from taking PTs. Refer to the Cambridge packs and curriculum as needed for the question types or topics you struggle with most as you go along.
That's funny that you mention that because I was going to ask if anyone had used the Cambridge Bundle. I would like to stick with 7sage as much as possible so that might be the better option.