I was torn between the T470 series and the X1 a few weeks back. I ended up getting the X1 and have been liking it so far. Got it with 16 GB RAM and the upgraded screen. Personally the screen was enough for me to chose the X1 over the T4xx series. Also the SSD is not soldered in and can be replaced, the RAM is indeed soldered in. Linux does run very well on it, didn't have any problems out of the box.

Edit: Although I wouldn't mind the T470 since one of my previous laptops was a T430 and I love the accessibility of that series.