Good Power Gamers - is there such a thing. I have been privileged enough to encounter one, just the one - for they are a rare and elusive breed . . .
How do I discern a Good Power Gamer - simple, I have encountered more varieties of Power Gamer than one could care to imagine.
From the Guy who makes himself feel powerful in the game by constantly badgering and bullying his fellow players, to the fellow who actually ADDS Hit Points of Damage taken to his Hit Points for every other hit (way better than a healing surge Lol), to the chap who fiddles and cheats and grubs each and every little minutia during games and during character creation . . . . .
Now, I'm not going to mention the names of the bad gamers - because I don't think that would be particularly fair - although simply from my descriptions they are going to realize who they are - except for the 'Hit Points Fellow' who passed away a number of years ago, which was a shame - because for all his faults he was a lovely bloke.
But back onto point, the Good Power Gamer - who's name is Andy. His 'Power Gaming Kick' came in with wanting his Characters to be the best and the most powerful they could be (One of his favourite Games was Metascape - it was a Power Gamers dream Lol). Even so, he NEVER attempted his quest for power at the expense of his fellow gamers.
Sure, he made unusual requests as a Player (he wanted a Cambion Character once) - but he was excellent as a Player. Even though Andy couldn't do voices, or accents - all his characters were different. With different goals and passions.
One of my favourites out of all his Characters was Nightshade (not Robin as I thought it was, Andy has since corrected me), a Thief under the Second Edition Rules - I even ran Adventures for Nightshade alone (whilst our Mrs' were nattering in the other room) - I wonder if he ever thinks about Nightshades Solo escape from the Prison at Guildstown - through the sewers no less Lol. Happy Days :-) (though technically not for Nightshade Lol).
So, as I wrote - there are Good (if not great) Power Gamers. You just have to be lucky enough as a DM to find one.