x240 and x250 no problem with 2 external monitors (keep in mind you do need the right docking station) and ubuntu 15.04, 15.10 and 16.04.
I had problems with the set up for the x260. Even with a brand new docking station. Not sure if I had a Monday-machine or if the hardware was conflicting. I did not get it to work with ubuntu 15.10 and x260 and docking station and two external monitors. Even after replacing the mainboard of the laptop (I had a technician come by and replace the mainboard after seeing some weird Intel errors).
Hope this helps. Would love to hear people's experiences with this x260 set up and with ubuntu 16.04.