keep & evolve both, 86% iv is awesome.
the IV only add 15 points to base values. so, if you got 15 on attack, your dragonite will have 250+15=265 attack. that's an overall attack bonus of 6%. those 6% are the maximum attack bonus you can get. you probably won't feel any difference between 100% IV and 0% IV while battling. 100% instead of 0% sounds like something big, but it isn't. it's much more important to have good movesets. i keep anything above 60% for gym battles.
Another dragonite question. Evolve 100% Dragonair?
Answers
Also that 6% might not even make a difference due to how damage is calculated, which rounds down every value +1.
e.g.if your move ends up doing 2.2 damage, it gets rounded to 2+1 for 3 damage. 6% more of 2.2 = 2.33 damage which still gets rounded to 2+1 for the same damage.
Charge moves that do more damage get closer to their actual increases though.
The Dragonair is level 10, so getting it to level 20 (the same as a Dratini from an egg, would cost 38,000 stardust and 38 candies.
But since evolving Dratini to Dragonair costs 25 candies, you're basically paying 13 extra candies and 38,000 stardust to have a better Dragonite compared to hatching a Dratini from an egg that will probably have around 80% IVs.
Lv 10 Dragonair -> Lv 20 Dragonair = 38 candies + 38,00 stardust
Lv 20 Dragonair -> Lv 20 Dragonite = 100 candies
So the total is 138 candies and 38,000 stardust.
Lv 20 Dratini -> Lv 20 Dragonite = 125 candies
I think 13 extra candies and 38k stardust is a small price to pay, and if you evolve the 100% Dragonair you can be sure that you won't get a better one.
Still, if you want to save those dust and candies, 86% is more than usable. The difference between 86% and 100% in CP is only about 50-70CP. The only thing that will have a higher slot than that 86% Dragonite is a higher IV Dragonite.
Definitely save up candies and evolve the 100%er.
Dargonite is currently the most bad ass pokemon in the game. And having a perfect IV pokemon alone is hard to come by, let alone having a perfect IV DRAGONITE!!
Whatever his moves, it is still a 100% dragonite. It will either be a beast for offense or a relatively good defender (damn you Lapras! ;) )