I happened to have collected all the quest HQ gear from 64 to 68. Here are some relevant values:
  • defense head + body + hands + waist + legs + feet (VIT)
  • Lv 60 270 Shire: 343 + 480 + 343 + 297 + 480 + 343 = 2286
    (VIT = 117+190+117+88+190+117 = 819)
  • Lv 64 273 HQ: 389 + 545 + 389 + 337 + 545 + 389 = 2594, meaning Shire + 13.5%
    (VIT = 120+195+120+90+195+120 = 840)
  • Lv 66 279 HQ: 482 + 674 + 482 + 417 + 674 + 482 = 3211, meaning Shire + 40.5%, or the Lv 64 set + 23.8%
    (VIT = 122+199+122+92+199+122 = 856)
I'm not familiar with the actual damage reduction from defense, so I can't offer how much actual difference they pose. But I'd wager there's a huge difference between someone at level 66 or syncced wearing their level-appropriate gear and someone at level 65 who only has access to the first two sets.