First choice is supposed to be like single-target-that's-an-artifact proliferate. I just didn't look up the actual wording right now as I'm in a rush.

The keyword should specify when you pay the overclock cost. Is it an activated ability? Additional casting cost? Alternative casting cost? Special action? Upkeep trigger? ETB trigger? Cast trigger? Does this maybe trigger whenever you pay on anything?

Overclock seems like it would be pest suited for a keyword action, so you can have wording like:

• ": Overclock an artifact you control. (Duplicate a counter on it, or give it +2/+2 until end of turn if it's a creature or give its equipped creature +2/+2 if its an Equipment.)"
• "When ~ enters the battlefield, overclock an artifact you control."
• (On an instant/sorcery) "Overclock up to two artifacts you control."

Your reminder text is too long to make this attractive, I partially addressed that above with the suggestion of the "duplicate" wording which seems grokkable enough that you could introduce it - at least for reminder text, but maybe it's something that can be pushed further. Not a necessary consideration for this sample card/mechanic.

But the real kicker would be the ability to shorten the second part e. g. "or give a +2/+2 bonus to it if it is a creature or Equipment." with "bonus" doing different things on creatures and Equipments.

I think, this mechanic is not feasible unless you commit it with a conscious change towards Auras/Equipments like this: Blessed Implements, which is within the range of things you could do as a custom card creator, but would be a major decision for Wizards.

Little late, as I a already included Overclock in a set. You also already commented on the mechanic in the set (though only with that the three modes were too many).

But, or "give a +2/+2 bonus to it if it is a creature or Equipment" and "Duplicate a counter on it" should shorten the text significantly and I thank you for that.

Edit: Nevermind this comment. I made a mistake when reading the card.