Thanks to the 145 ATK fist weapon and the 50% materia coming with the trial, it's actually better (ATK wise) to give your Orlandu Use Grappling weapon and champs belt.

Assuming full non limited bis (so no infernal harmlet):

Orlandeau 6 Star
FFBEDB Unit Calculator
Right Hand: Excalibur 120ATK Light Element
Head: Black Cowl 28ATK 25DEF 25SPR 100%Sleep
Body: Brave Suit 51DEF 15%ATK 15%MAG
Accessory 1: Genji Glove 10%ATK/MAG & Dual Wield
Accessory 2: Champion's Belt 30ATK/DEF & 20%ATK/DEF w/ Fist weapon
Ability 1: Use Grappling Weapons Can equip Fists
Ability 2: Large Sword Mastery 50% ATK w/ Great Sword
Ability 4: Wisdom 30%ATK 20%HP
Pot Stats: HP: 390 MP: 65 ATK: 34 DEF: 26 MAG: 26 SPR: 26
Esper: Odin HP:5450 MP:3955 ATK:6250 DEF:4310 MAG:2075 SPR:2270
Total Stats: HP: 6071 MP: 246 ATK: 760 DEF: 299 MAG: 208 SPR: 189

Since the calculator doesn't have either the weapon or the mastery, bear with me.

Orlandu fully potted have a base ATK of 189, 50% of 189 is 94.5, assuming it doesn't round up so it's 94 ATK, 20% of 189 is 37.8, once again I'll assume it doesn't round up, so 37.

Aigaion Arm is 145 ATK. So, with that build, once you equip Aigaion Arm, you will gain 145 37 94 = 276 extra ATK.

Which land us at 760 276 = 1036 ATK.

For those without Genji glove/Brave suit, you'd have:

Orlandeau 6 Star
FFBEDB Unit Calculator
Right Hand: Excalibur 120ATK Light Element
Head: Black Cowl 28ATK 25DEF 25SPR 100%Sleep
Body: Monster Breastplate 12ATK/MAG 46DEF
Accessory 1: Champion's Belt 30ATK/DEF & 20%ATK/DEF w/ Fist weapon
Accessory 2: Champion's Belt 30ATK/DEF & 20%ATK/DEF w/ Fist weapon
Ability 1: Use Grappling Weapons Can equip Fists
Ability 2: Large Sword Mastery 50% ATK w/ Great Sword
Ability 4: Dual Wield Equip two single handed weapons
Pot Stats: HP: 390 MP: 65 ATK: 34 DEF: 26 MAG: 26 SPR: 26
Esper: Odin HP:5450 MP:3955 ATK:6250 DEF:4310 MAG:2075 SPR:2270
Total Stats: HP: 5268 MP: 246 ATK: 698 DEF: 324 MAG: 182 SPR: 189

40% of 189 is 75.6, since we are not rounding up, it's 75.

So with Aigaion Arm you'd gain 145 75 94 = 314 ATK

Which land us at 698 316 = 1012 ATK

TL;DR: Supposing you can do the trial, 1k ATK Orlandu is in your reach!