...One of NASA's most stressing requirements is limiting the loads placed on a crew during an abort. Because Delta and Atlas fly "lofted" trajectories, these loads will exceed NASA's limits while the second stage is firing. Instead, NASA wants a booster with a lot of thrust on the first stage so it can fly a depressed trajectory that avoids the unacceptable abort loads. The 5-Segment SRB that now forms the first stage of Stick puts out around 3,272,000 pounds of thrust; Atlas V has 931,000 pounds in vacuum, and Delta IV a wimpy 743,000 pounds in vacuum ...Still, Stick will probably have the thrust excess needed to fly the depressed trajectory NASA wants.
I find this whole abort load requirement to be really interesting. So much work and engineering going into a scenario that has never really happened to my knowledge ever. Correct me if I'm wrong, but I don't remember a launch abort ever being done in the second stage of any NASA manned launch vehicle.