The OP is too reductionist. Can you define what metagaming actually is? And where it stops and powergaming begins? And whether there are divisions or grades within these categories?
Personally, the idea of pulling up an FAQ as I'm starting a new RPG and taking advice such as 'Take X trait, put all your creation points in Fire Magic, go to the town, sell all your starting equipment and buy a fire staff, you've now broken the first half of the game' is loathsome to me. It robs me of the joy of experimenting with the game's systems and seeing what the challenges are, and how I can best overcome them with my limited early resources. That fun is gone, unless I intentionally choose a sub-optimal strategy or otherwise attempt to limit or handicap myself.
But on the other hand, say I were playing something like Wizardry or Etrian Odyssey, something in that vein, and there's a long minefield maze I have to pass through with no way of detecting mines other than walking into them, and the mines cripple or kill my party and inevitably force me to reload or return to town after stumbling into only a couple of them. A maze with no in-game way to map it other than trial and error, with the expectation that I spend the next hour or so tortuously eking out a map in my characters' blood just so I could pass it. No resources are being expended, I'm not discovering anything new (or if I am it's at a snail's pace), and no challenge is being offered - my time is simply being taxed. So would I not want to look up a map online to quickly get through this minefield? I'd have conflicted feelings about it, but it certainly seems more justifiable. Is that metagaming or something else? Yes, that scenario focuses on exploration rather than combat, but it similarly going outside the game to find a 'shortcut' to what the game is offering as a challenge, just as an overpowered combat build is.
And then of course there's the problem that you often can't tell if a puzzle or challenge is 'fair' until after you've passed through it. What if after failing to navigate a maze of 'random' traps the first couple of times I reach for the guidebook only to discover that I misinterpreted a clue I found on an earlier level, or simply didn't find a nearby switch to disable the traps? The same can occur in terms of combat as well, just substitute the trapped area for bosses that require an understanding of their mechanics or a particular trick to beat, and the player, rather than working that out himself, bypasses this with an overpowered build gleaned from some FAQ.
In practice, I think it's rather easy to avoid extreme cases of metagaming and powergaming should you be so inclined, but if you want to actually have an in-depth discussion about it then you can't do so without also discussing what the player expects in terms of games providing a 'fair' challenge and not wasting their time. And then you have to take into account whether it's a game that 'expects' save-scumming or reloading (and then get into whether that itself is a good or bad thing - I personally believe it's bad).
An interesting addendum to the question in the OP would be asking posters what they did with their characters' stats in the EotB and Gold Box games. Did they Modify their rolls until everyone was an 18/00/18/18/18/etc demigod? For my part, when I was a kid: Yes. When I've attempted those games as an adult: No.
