they are not resetting justice points, only capping them at 4000 for patch 4.03
currently the quest rewards for a fresh 80 are 272 greens. These have about the same stats as a 264 epic but are missing set bonuses and often sockets. I would say it is accurate that by 81 you will replace most of your raid gear, if you are decked in 277 you may last until 82. It took me about a day of very idle play time to get to 81.