usually, if smogon fails me, i decide to do tsomething on my own. And i believe that kingdra can ditch 15 spe (60 EVs) and still outspeed (in rain) a +2 Dragonite. Alternatively, you can ditch 10 spe and outspeed dragonite (nature/252) with no speed boost.
If you go full 252 speed, then you outspeed Haxorus.
252 is optimal i think.
That's all i can do. XD