Outside of the Ring Fering found, no spellcasting magic item will allow you to "upcast" the spells as Mythic.
Specifically, magic items that cast spells (wands, rods, scrolls, staves) do not benefit from any ability that "affects your spellcasting". See this FAQ:
Does using a potion, scroll, staff, or wand count as "casting a spell" for purposes of feats and special abilities like Augment Summoning, Spell Focus, an evoker's ability to do extra damage with evocation spells, bloodline abilities, and so on?
No. Unless they specifically state otherwise, feats and abilities that modify spells you cast only affect actual spellcasting, not using magic items that emulate spellcasting or work like spellcasting.
"But wait! ShadowKras pointed out that Staves are different."
Staves have two specific exceptions (as per the FAQ's "Unless they specifically state otherwise"), neither of which Mythic :
use the wielder’s ability score and relevant feats to set the DC for saves against their spells... can use his caster level when activating the power...
Also, from Mythic Magic:
Mythic spells can’t be crafted into magic items unless the item is an artifact (for example, you can’t brew a potion of mythic cure light wounds).
Additionally, this isn't directly related but further supports this conclusion:
When casting a spell from a scroll, wand, or staff, can I apply one or more of my metamagic feats to that spell?