Quote from GreetingsGQ >>

Quote from Fangeye >>

7) Increasing in size category does not intrinsically increase your damage. The +1d4 is an effect of the Enlarge/Reduce spell. Note that Giant's Might gives a different bonus to damage that is independent of the change in size, and the Cape of Enlargement does not change your damage at all.

 

Cape of Enlargement 

• When you hit with an attack roll using a weapon or an unarmed strike, you can add your proficiency bonus to the attack’s damage.

 Thank you! I edited my post to fix the error.

I want to take a fairy to the max size. level 10 is the max I can go though so far I have the barbarian path of the giant. gets me from small to large. Then the enlarge reduce spell to go to a huge follow by a potion of growth to go gargantuan. I just want to push one more size. any ideas?

You could always just craft an oversized weapon for just such an occasion.

Quote from Growlshorttusk >>

I want to take a fairy to the max size. level 10 is the max I can go though so far I have the barbarian path of the giant. gets me from small to large. Then the enlarge reduce spell to go to a huge follow by a potion of growth to go gargantuan. I just want to push one more size. any ideas?

 There is no size category after Gargantuan in either 5e or 5.5e