Take 2 Mienfoos : Chan & Lee
Chan is holding te Power Bracer while Lee holds the Macho Brace.
Each faces One(1) Patrat, which gove 1 Attack EV each.
Chan will gain 5 Attack EVs, 1 from Patrat, 4 from the item
Lee will gain 2. The Macho Brace takes the EVs from Patrat and doubles it so 2.
If PokeRus was involved, Chan would gain 10 while Lee gets 4.
So in conclusion, Power Items for the win!