Survey about IV% and evolve/powering up

depends on species (utility and ease of getting candy) and CP
a level 30 eevee with 82% is going to get evolved for sure.
an 82% dratini is probably not going to get evolved. because the candy is to rare (unless you have gotten to like 250 candy)
an 82 gyrados is not because with a little patience surely you will do better (unless it is shiney)

For me:

Common stuff like eevees/bulbasaurs/eggys/Magikarps: All >91%
(especially magikarp- if you have to catch 100 of them just to evolve 1 gyarados, chances are at least 1 has to be >91%)

Rare stuff
Dragonites/ Tyranitar/ Lapras/ Snorlax/ Chanseys: I'll take it if its more than 85% with A-rated moves.

If it is for offense only (Machamp, Jolteon, etc) where IVs don't matter that much, I set the limit at 70% and higher.
If it is for defense, I evolve whatever goes higher in CP as long as it is 82% or higher, and power up if the moveset is good enough.
There are 4 exceptions to this:
- Blissey and Snorlax, because they are good on their own.
- Dragonite and Tyranitar if they have good defensive movesets, because even a 70% specimen will rise above pretty much any other Pokemon beside a better Dragonite / Tyranitar when it comes to CP.

If the candies are rare and I really need one, I pick the one with the most IV whenever it is more than 50%. If not, usually at 75%.

For a defender...then the IV is important. I have exceptions that were wild catches at a high level that have used very little candy/stardust to get to a good CP and level - but if I am trying for a defender then I will use the best IV I can (usually 90%+)

For attackers, I am less choosey, and will happily take a lvl30 mon with reasonable IV (above75%) and try for the moveset I want. This way I can get an immediate attacker in my lineup without the need to use valuable stardust or candy.
It can be frustrating to get a high IV mon to evolve with a good moveset and then still need to wait for candy to put it to a level that it is an effective attacker.

This way, if I get a better IV level30 mon at a later date, I can evolve another and get an improved mon of the same moveset, to add to my roster...and I will still have candy as I haven't wasted it levelling up a lvl20 mon to lvl30.

TL/DR For defender then IV is king for me...for attackers, I would rather a high level to make an immediate impact without the expense.

The answer isn't as simple as "what percentage IV is the cutoff line between evolve or not evolve." That's sort of like saying, "in football, at what yardage do you punt or try for a field goal." Many other factors come in to play beyond the number.

If I'm swimming in candy, anything Spark says "can battle with the best of them!" or "is really strong!" gets evolved.

Otherwise, once I've saved up enough candies, I'll generally pick the best one I have (depending on IV's and level) and evolve that, as long as I have one over 80% IV. Otherwise, I'll wait until I do. So 80% is my cut-off for anything that isn't super-common.

Not that simple. I believe the level of the Pokémon and rarity os candies also matter. For example, when gen 2 launched I had same great IVs level 20 Chansey and 1 level 30 with 77%. If I evolved 2 level 20 I'd not have candies to power up both, so I evolved the level 30 and evolved end powered up the one with highest IV ending up with 2 usable Blissey.
For common Pokemon like Eevee, I simply evolve every high level Eevee, since they are great attackers at levels 28-30.
For most ones, I try to balance IVs and levels, like a 75% level 30 is most likely getting evolved than a 84% level 20, except for Dragonite, Tyranitar, Gyarados and Rhydon where the highest possible CP is the goal.

As for powering up, movesets rule for most, except those with highest possible CP. Even my 100% IVs will remain forever in level 20 if they came with bad movesets.

I tend to power up only 95%+ IVs Pokemon with the perfect moveset. As such, I have only powered up 5 Pokemon to date, with 2 million unused stardust. I wouldn't recommend playing like this lol.

93%IV or better is my general rule. If it’s rare for me I might take something below that or if an A/B move set become a legacy set.

I also have a 93% cutoff, but I don't battle in gyms every day. I made exceptions for mons that I might never get a better one for a long time (lax Fully powered at 78, 80, 82), (lapras 89, 84) or desperately need another gym defender. I made one exception for jolteon because until yesterday, I never found an eevee over 91% after catching 1,200.

Generally I try to power only 90% or high but when I got my first Lapras at 88% with Frostbreathe/Blizzard as a move set I was so happy I powered him. So happy I did. Over 5 months later I never got a better one and he's a great Dragonite killer. So it really depends on the situation and your needs.

Ill evolve anything thats 82% or over, maybe put it to 30 (depending on the investment to get it there, move set, rarity etc), however past 30, 90% + with a moveset I am happy with, generally A, maybe B rated depending on the poke and it's uses.