Both batteries will be better than the 5 series but I think the Plus will really be solid.
I am eager to see what the battery life on the Plus will look like in the real world. I too think it will be an improvement.
It most definitely will. Its a bigger phone, so they have more room for a bigger better battery. I mean look at the iPads. You can get like 14-18 hours of usage and charge them every 2-3 days. They are amazing.
What will really sell me more than anything is if the batter is significantly longer. I don't wanna be carrying around portable changers anymore