For these calculations, the target is a level 50 Zangoose with 31 IVs, 0 EVs and a neutral Nature for Special Defense.
Choice Specs Calculation: 232-274 Damage
This will make your Special Attack stat 307, which is 41 more than your Special Attack with a Life Orb. This will also do 29 to 35 more damage than our Life Orb calculation.
252+ SpA Choice Specs Adaptability Porygon-Z Tri Attack vs. 0 HP / 0 SpD Zangoose: 232-274 (156.7 - 185.1%) -- guaranteed OHKO
Life Orb/Normal Gem Calculation: 203-239 Damage
This will make your Special Attack stat 266, which is 41 less than your Special Attack with Choice Specs. This will also do 29 to 35 less damage than our Choice Specs calculation.
252+ SpA Life Orb Adaptability Porygon-Z Tri Attack vs. 0 HP / 0 SpD Zangoose: 203-239 (137.1 - 161.4%) -- guaranteed OHKO