The article would indicate that the highest one can reach is +5 steps. There is a sixth step noted, but it's only examples are moves that automatically crit.
If I understand this, though, one can breach step 5 without cheating. Example:
Your pokemon has Super Luck(+1) while holding Scope Lens(+1). You use a Dire Hit on him(+2) and choose a move with an increased critical hit(+1).
That would be 6. (Base 1, +1, +1, +2, +1 = 6)
So, does this mean that you CAN crit every time with an increased priority move on a pokemon with super luck? Or, does the game just ignore any steps beyond 5?