So I Think I was experiencing the same thing. I have an x1 carbon 4th gen with Skylake and an NVME drive.
I'm still running 4.4.0-23 *(ubuntu kernel). I was only able to get to pc2. I ended up booting into windows to debug a separate unrelated issue, and ran a few updates. I had already been running the 1.14 bios and firmware revision 1.9 so that wasn't the solution. I did upgrade the IMEI firmware though. After rebooting back into linux I'm now getting much better behavior.
Re: NVMe problems
So I Think I was experiencing the same thing. I have an x1 carbon 4th gen with Skylake and an NVME drive.
I'm still running 4.4.0-23 *(ubuntu kernel). I was only able to get to pc2. I ended up booting into windows to debug a separate unrelated issue, and ran a few updates. I had already been running the 1.14 bios and firmware revision 1.9 so that wasn't the solution. I did upgrade the IMEI firmware though. After rebooting back into linux I'm now getting much better behavior.
C2 (pc2) 12.6%
C3 (pc3) 0.1%
C6 (pc6) 55.4%
C7 (pc7) 0.0%
C8 (pc8) 14.8%
C9 (pc9) 0.0%
C10 (pc10) 0.0%