thebest, that information is incorrect. Power Items actually give +4 to EV gain. I will again use Magikarp as an example.
Magikarp gives 1 Speed EV, if the pokemon that gains exp from defeating that Magikarp is holding a Power Anklet, it gains 5 Speed EVs. Further, if it has Pokerus, it gains 10 Speed EVs.
Formula:
[1 (Base EV gain) + 4 (Power Item) ] x 2 = 10 (final EV gain)
Now, divide that number by 4.
10 (EV gain) / 4 = 2.5 (actual change in stat)
By defeating one Magikarp with pokerus and the Power Anklet, you have actually gained 2 points in the speed stat. (the .5 does not contribute to a stat point)
Were you to defeat anoter magikarp, you should have 20 EV points, which is 5 stat points.
A pokemon can only have 510 EV points, with a max of 255 in any one stat.
So, the EV spread for a typical sweeper, I'll use SDLucario as an example, is the following:
252 Attack/ 252 Speed/ 4 HP
Because the max EVs in any one stat is 255, you waste 3 EV points if you max it out (since you have to have 4 EV points to contribute a stat point).
So, in a set like this, it's typical to use those last 6 EV points to add 1 Stat point somewhere else.
In other matters, what do you have anything interesting to give me?