I know that if you have multiple items equipped that give the same damage bonus that they stack. But I was wondering: is there a limit to this?

The most I've seen is "ultra" and that was with a Super Slime Slasher and a Wolver set. I'm assuming "ultra" is just above "high" so it'd go:
Low > Medium > High > Ultra?
But back to the question. Is there a limit on this? Does it go above ultra, and if not, would damage bonus still stack even though it says it's at ultra?
The reason for this question is because I'm going to make the Skolver set which both Cap and Coat give "Sword Damage Bonus: Medium" and I want to make the Barbarous Thorn Shield, which also gives "Sword Damage Bonus: Medium".

If it only adds Medium + Medium from the Skolver stuff and doesn't add the Medium from the shield, I'll probably just go for Owlite to complement my freeze defense armor.