You wont see a threat loss from one item change. Realistically your threat primarily comes from using your abilities correctly, followed by spec/glyphs, and MD or Tricks. Expertise and Hit are bottom of the barrel in threat generation.
When considering an upgrade as a tank these days your only concerns are Armor, Health, and number of sockets you can stick +30 stam gems in. If the upgrade has more potential to increase your EH (armor +stam) its worth using.
There is something so appealing about backhanding someone across the face with a shield.