Here are the facts regarding the Ykeshan Hoop of the Pestilence, in regards to actual gain that you and the pet receive.
Numbers will vary depending on your base damage and your pet's base damage of course. For the record my pet had +770 spell damage and 20% base damage, while I had +740 spell damage and 26% base damage (higher base damage
will increase the gain to us).
Before is on the left, After is on the right. Remember that the Ykeshan Hoop does
not affect the DoT damage, since it's +Spell damage and not +Base damage.
Solidify: +110 on the top end
Vampire Bats: +193-290 to initial tick
Effigy: +252 to initial tick
Crystal Blast: +77 to top end
Winds of Velious: +484-591 to initial tick
Blazing Manifestation: +33 damage on the top end per hit (spread among all hits)
Shattered Tectonics: +133-162 to initial tick (AoEs reduce effective gain by 1/3)
Earthquake: +118 to top end (AoE)
Torrent: No change (capped)
Master Strike: +361-442 damage
Bewilderment: +266 to top end
Shocking Flames: +47 damage to top end (AoE)
Sphere of Flames: +48-273 damage
Searing Flames: +82-284 to initial tick
Wave of Flames: +16-91 to initial tick (AoE)
Blazing Conjurations: +262-393 damage
Storm of Flames: +91-152 to initial tick (AoE)
Minion's Mark: No change (capped)
Igneous Flames: No change (capped)
So as you can see, it's not a huge overall boost to DPS to even the pet.
To really take advantage of it you need significantly more base damage than I used in my test, and at least two in your group (presumably a Sorcerer in the group will be wearing one, since they benefit greatly) so that the proc is up more often.
In my experience though you'll get more personal DPS wearing just about anything else, in particular Ferzhul's Earring of the Void, Talisman of the Ethernauts, Hoop of Deadly Destruction, Earring of Hollowed Darkness, or Darkened Jewel of Poisonous Fire. However you'll likely get more raidwide DPS if you're grouped with at least one high-parsing sorcerer (or even 2 high-parsing sorcerers), since they benefit greatly from the proc on the Ykeshan hoop.