If you've already seen all the bosses at least once, I highly recommend doing Endurance, and collect from the chest after EVERY boss. Skip annoying bosses like Dag mother, desert treasure, the Illusive, etc. by using the exit stairs. That's the fastest way to get journal pages, and trust me you don't want to have to go back to the tower after 500 kills just to hunt for journal pages. Climber is a LOT slower, and the tiny bit of XP from books is simply not worth it. If you don't want journal pages, do Endurance and keep going until an annoying boss, then restart.