The test results are in, and it appears the new $399 iPad 2 has better battery performance than the 2011 model. The endurance boost seems to come from the new 32nm A5 processor found on the new crop of units, each designated iPad 2,4.
Anandtech managed to snag an iPad 2,4 and performed the tests, finding significant improvements, including a 15.8% boost when web browsing, 18% when watching video, and 29% when playing high-end games.
So how can one ensure they snag a new iPad 2,4? Unfortunately, there is no way to determine whether an iPad 2 has the old or new processor without opening the box and powering it on. However, the new, power-efficient iPad 2s should begin replacing the older crop as time goes on.