I can confirm that this works on Sony Xperia Z (C6606). I flashed from the latest T-Mobile 4.1.X (i forgot) to Greece 4.2.2. Still maintains 100% functionality. 4G LTE is still available. This would be the recommended FTF for all those T-Mobile Xperia Zs with locked bootloaders. In FlashTool though, I checked exclude Baseband.
This firmware does come with a lot of bloatware though, including Mcafee, wisepilot, neoreader, and several others.
This was done with flashtool-0.9.13.0-windows.exe
When phone booted up it actually gave me a selection of either USA or Tmobile and I chose tmobile and it downloaded the settings for SMS/MMS. everything is working flawlessly, thank you for the post.