What is your minimum IV, to max out or get to level 30 threshold?

Minimum IV would be 80 IV with 15 atk at least and the species better be damn useful to get maxed. And I max past lvl 30 anyway.

I'm in the long process of finally maxing things. Rare candy is the toughest part, 15a/13/15 Dragonite maxed. 100% Tyranitar maxed. 14/15/14 Raikou maxed. Level 39 on a 15a/11/15 Mewtwo. Level 38.5 on 15/12/15 Kyogre. 100% Gardevoir at 36, will max when I hatch a few more Ralts. Probably another Tyranitar which is at 35 and 96%. Another Dragonite a 36 and 15a/13/14. Walking Bagon and have a 96% 15a/14/14 Salamence at level 33. About all that is on my maxing schedule right now. Eventually Groudon, but it is only at level 32 (91%) rare candy goes many other places***as long as the IVs were at least 84ish, I would max my best Raikou, Mewtwo, Kyogre, Groudon. MAYBE Rayquaza but if it was 93% with 14 or 15a.

For me, it's 14-15 ATK and 91%+ IVs overall. As long as your ATK is at least 14-15, you'll almost always hit all the major breakpoints with your quick move, and stat distribution with DEF is enough that you'll hit most major bulkpoints, too.

Mine is anything over 88% IV, anything less gets binned off.

75% IV, 14-15 attack. Except for certain Pokemon where any >75% will do.

For legendaries, my best one at the end of the month.

82+% IV with at least 7 attack.

Depends on species, availability and current level (though not as much), but I typically transfer anything less than 87-91. Higher level/rarity leads to more flexibility. I generally look for double digits in all stats. I powered up an 80% Mewtwo (15 attack/10/11)

Level 30: Wonder and useful species.
Max out: Yet to do so, but will consider once I reach level 38. Only strong candidate is my 98% Machamp.

Only legendary I maxed is my 100% Groundon. Zapdos 91%, Moltres 96% , Entei 89%, Raikou 93%, Lugia 93%, Kyogre 91% standing at lvl 35,5 with no intention to power up further. Ho-oh 96%, Raikou 96%, Groudon 98%, Rayquaza 98% standing at lvl 31,5. Eventually Raikou will be pushed to 35,5 too. Then a double flying 96% Rayquaza will be pushed to lvl 31,5 as well. My Mewto obtained yesterday will go to lvl 31,5 too as soon as I get more candy.

As for non legendary pokemon I still wait for a good Metegross and hope to land one 100% to max it out. Other projects atm are both 100% Machamp and Golem which will get maxed. Normally my cutline sat at 76% for already high level pokemon, but I would say that now it is more like 84% 15 attack or 87%-91% depending on rarity to invest dust into a pokemon.

I max out a lot more than most people.

I usually stick to this:
For Mewtwo: First 3 , no matter IV (and 67% aint bad in practise)
For legendaries: 1-4 of best ones (lowest IV so far 84%)
For useful species: usually 96%
For those I early on invested a lot stardust in: About 75%
Cool legacy moves: No limit (34% Body slam Snorlax)

The minimum IV changes based on how much I need that pokemon. If the mon isn't that relevant, it needs to be 100% for me to even consider powering up. For most relevant mons, I'm looking for at least 93% 15a/96% 14a. Treshold can be lowered for a variety of reasons which include access to valuable legacy moveset, high level catch (ie. small dust cost to max), low chance to obtain a better one etc.

I rarely power up to 30 nowadays, since it won't make any of my attacking teams at that level.

For legendaries, I power up whichever is the best IV that I have after the legend rotates. So far they have mostly been fairly acceptable.