Just bought an X1 Extreme gen 2, and immediately upgraded (aftermarket) to 64GB of RAM and 2x 1TB M.2 drives. Feels pretty good. Ubuntu install was very smooth. The only thing I hate is the super cheap-feeling keyboard.
The Extreme looks great on paper but I'm not sure I want to go up to that size of laptop. I'd have to handle it to figure out. Nvidia graphics make it a non-starter for me right now though.