this is wrong mate : i loaded my old savegame file where i did not get this buff and did the quest to test something:
at this time is was already at 1475 armor with full deadric without shield. (with ALL heavy armor perks and smithing 130% etc. and lords stone active) after i got the buff the difference was HUGE. so its not base armor increase it works the same as the perk one where you have to wear a matching set for example.
after i got the buff i had 1727 armor rating. so its power increases the higher your total armor rating gets. its nearly over 250 additional armor with the buff (only counting the ARMOR bonuses) with the additional smithing bonues these numbers would have been higher again.
Hmm, I only did testing on a couple of pieces so it's possible that the numbers were too small to give a proper indication. I'll do some more testing with bigger numbers and see exactly what it effects.
Edit: My original testing for reference;
http://www.gamesas.com/index.php?/topic/1289727-2419-armor-6399-damage-using-smithing-alchemy-enchanting-only-33-perks-329k-backstabs-post-4/page__view__findpost__p__19554461
Edit:
Armor skill doesn't effect it except for a minute amount which I believe is simply the effect of rounding, here's my numbers
Full Daedric armor
Skill - Armor = With perk (Percentage) (increase)
100 - 205 = 239 (16.5%) (34)
75 - 189 = 224 (18.5%) (35)
50 - 175 = 213 (21.7%) (38)
25 - 160 = 198 (32.7%) (38)
0 - 144 = 182 (26.3%) (38)
Deadric Chest only
100 - 69 = 81 (17.3%) (12)
0 - 49 = 62 (26.5%) (13)
Will test perks and smithing upgrades next.
Edit 2:
All armor perks effect the boost;
Full Daedric Set, 100 Armor skill
Perks - Armor = With perk (Percentage) (increase)
0/5 - 205 = 239 (16.5%) (34)
1/5 - 235 = 274 (16.5%) (39)
2/5 - 266 = 310 (16.5%) (44)
3/5 - 297 = 346 (16.4%) (49)
4/5 - 328 = 382 (16.4%) (54)
5/5 - 359 = 418 (16.4%) (59)
1/1 - 448 = 522 (16.5%) (74)
1/1 - 538 = 627 (16.5%) (89)
Edit 3;
Smithing boosts are adjusted by the perk,
Pre-improved Deadric armor
Unimproved - 205 = 239 (16.5%) (34)
Improved - 272 = 321 (18%) (49)
Edit 4;
Fully improved daedric set with 4x29% smithing gear, 130% potion and all armor perks
1597 = 1881 (17.7%) (284)
Then improved again after getting the perk;
1881 = 1980 (5.3%) (99)
Total Improvement;
1597 = 1980 (23.9%) (383)
Conclusion; For pure numbers, this perk is pretty amazing. Almost a 400 boost just from this perk. For Min/Maxers it's just as awesome, saving them at least one perk point when trying to hit the armor cap. There's really no reason not to get this perk ASAP.