I REALLY liked the form factor on the 5S. Even though I've gotten used to the size of the 6 and 6S, I still wouldn't mind the form factor of the 5S again as it was so easy to one-hand. That said, it's the little things that have me hooked on the 6S now... believe it or not, the apps I use that have taken advantage of 3D touch have me hooked. For example, I can deactivate/reactivate my home security cameras like that (*snaps fingers*) thanks to 3D touch. Those little things have me hooked, even if it is a gimmick the other 80% of the time.
And I don't think it's 100% guaranteed, but by the lack of info out there, I'd put my money on it being about 99% that the SE has 1gb of RAM instead of 2gb.