I'd say that to really get to the point where you'll be out there doing all sorts of stuff and generally having a big impact on the world, you'd probably have to get to 4th-6th level. At that point, you'll be able to do targeted strikes against the mega-corps that can actually make them do more than yawn and say "Oh, someone actually bothered with that?". I mean you could do that before then, but it's unlikely to happen on a regular basis until then. They're just too fragile to raid well defended bases owned by people that can send armies after them, especially when they (literally) are the police. As far as magic items, that would depend on whether we had a Shaman, a City Shaman, or a Hermetic Mage with us, if we had a spellcaster at all. We'd probably have some good cyberware by then though. Also, we'd probably be going up against a good mix of HMs, Riggers, and mid-level Deckers, not to mention the Street Samurai.
For me (playing LL) the break point is 9th-10th level. You reach the summit of natural human ability (implied by hit dice per level dropping to set hp adds), settle down in your shiny castle, bully the local monsters into signing up with you or moving on, and generally become Lord of All You Survey.Anyone who goes beyond 10th level IMG has made some sort of weird Faustian pact for power. As they continue to accumulate arcane secrets and personal might they slowly become less human and more Other. This means the high-level scene is rich in Ice Queens, mages with hidden hearts, Worms That Walk, Awnsheigh, Conan-style Evil High Priests, and a bunch of people who wield thunder and lightning as weapons or have replaced parts (or all) of their body with Significant Artefacts.At this level probably the biggest threats to the Powers That Be are the conflicting agendas and rivalries of the other Powers That Be, oh, and the race to gain Wish power and/or ascend to godhood. Raiding Orc tribe? Yard trash: send some Name Level barons to deal with them. Rogue wyvern pack? They'd make great mounts for your new unit of aerial cavalry.The Three-Crowned Queen of the Winds is stirring up the giant tribes to block your access to the [portentiously-named locale of arcane power] right before the Grand Conjunction? Sly b*tch! It's about time you did something about her. Fortunately your otherworldly sponsors are hinting that her power can be weakened if you can only [plot hook for convoluted revenge/power-grab scene using an unsuspecting pack of adventurers as deniable cat's paws].Dragon on the rampage? Nice change of pace from politics. Round up the guys...
Oops. Note: I'm using Shadowrun 1e, so that may make a difference. It's been a while since I got a chance to play D&D in any form. There the monsters they face will be things like the Duun'Variin - in other words, weird things that only vaguely resemble the creatures found in the Monster Manual.
I've always felt the "sweet spot" for adventuring was 4th-7th level. 8th and up is pretty much "powerful," and I've not really done a lot of gaming in that zone.
A "powerful" NPC is my Dwimmermount campaign is one that's level 9+. To date, I've only definitively introduce three such NPCs.
Powerful would be a Conan or an Elric of Melnibone type. There have only been two players in my campaigns to rival such feats, and they were 18th and 15th level respectively. As for powerful, the adventurers fought Arioch, Duke of Chaos, on the spire of Sigil with artifacts including the soulstealing sword Mournblade, the Holy Avenger Excalibur, and the Runestaff. Arioch was "destroyed" and Sigil was brought down to the base of the Spire. End of days stuff. On the average, high powered players are 10-12 level. They fight demonspawn, devilcults, liches, etc with an occasional hop to distant lands around my world. Able players can do so much, they do not need godlike levels to have fun!
A truly "Powerful" is in the 9-12 ranger for me.
"Really powerful" in my campaigns tends to mean someone from 7th to 11th level. Of course, even a party of 5th level characters is a considerable force in a lot of areas - not people who can get away with anything (a bunch of 2nd or 3rd level guards can still pose a serious threat for a party like that if they get badly outnumbered), but people who can get away with a lot.
The high kings, the emperors, the high priests; they're usually epic level. I like representing the game's whole range of levels in the campaign, even if the party is only at 13th level right now. I figure in a fantasy world, powerful characters either start immortal, or figure out how to gain immortality. As a result, there're quite a few epic level immortals hanging around an ancient world.As to what they do? Well, most of them are patriarchs and matriarchs of entire dynasties so they spend a lot of time plotting and competing for resources. And when a major demon lord or an ancient wyrm goes on a rampage, who else will kill such powerful monsters and take their stuff?My 13th level party just handled a dungeon full of moderately powerful demons, but they'll get to the big leagues some day. As to what they have; mostly magic weapons and junk that help them kill things faster. I'm not much into items, so I don't write many mcmuffins or plot device artifacts.The party fighter did decide to capture a lightning demon during last adventure so he could channel its power into his forge though. I haven't worked out how well that's actually going to work yet.
Powerful is 9+ in my campaign, as with James'.The PCs are level 5 to 7 at the moment, which means they're on the cusp of serious power, but they don't really realize it because most of the time they play by the rules and aren't consciously testing themselves. I think they'll realize soon, though, that there aren't a whole lot of folks running around at their power level.I've introduced a handful of 10+ NPCs (maybe five), two of whom are set to retire or die fairly soon (both 10th level), and one of which is a major enemy figure for the campaign (and 12th level).Several of the characters in the party are carrying quirky unique magical items, though only one that might be considered an artifact, though it hasn't been awakened/activated in any significant way yet, and the highest bonus on any weapon/armor that anyone's carrying is +2.Perhaps the most powerful fully-functional item anyone in the party is carrying is a helm of limited true sight.
9+It's in the math.By the time they hit level 7 they are maxing out the xp per adventure. They will never earn more (no matter what they do) then about 20k a piece split. And since the xp range caps out at around 200-300k a level when they hit level nine, it takes about a year to get there, and if you play once a week, six months (6x4 = 24*20k = 480k) to gain a level (with missed sessions and only getting xp at the end of adventures taking a few weeks to run). So, 9th, simply due to how long it takes to gain levels.
Yes, 9+ . . . even level 7-8 PCs can get a bit tricky to challenge or kill . . .
Non-heroic game (inspiration Chainmail, so 0-3rd lvl., 3rd lvl. being the most powerful (hero-1), AD&D 1st ed. is the platform but it's homebrewed with elements of OD&D and Classic Editions. Weapons of quality (see Samurai NPC/Best of Dragon)spellbooks, and items that improve # of spells/day or morale top the rarest and most desired lists. As for adversaries, pretty much opposing O-lvl man types (cult followers and priest, men-at-arms, brigands and underworld types, and NPCs, with a weird nasty thrown in if they venture to the edge of the world).
7th-10th, with 9th as Name Level where you're a living legend.