well techinically the power would be like this: 40x1.5(stab)=60x2(huge power, yes I know its his attack that gets doubled but the amonunt of damage he does is the same)=120x.20(splash plate 20% boost)=144 but that would make 144 power with 218 atk
If you decide to go the other way he has 436(Huge power boost already applied) attack with 72 power(60x.20(splash plate)) but their techinically the same amount of damage either way
EDIT: Also if you really want to sweep/revenge kill with aqua jet, I suggest choice band over splash plate. That would make 40x1.5(stab)=60x2(huge power)=120x1.5(choice band boost)=180 power with 218 atk
If you decide to go the other way he has 654 attack(436x1.5 (choice band)) with 60 power aqua jet. But again, theyre pretty much the same damage youll do.
If you want even more power, use it under the rain which will make it the equivalent power of 270 power aqua jet with 218 attack.(40x1.5(stab)=60x2(huge power)=120x1.5(choice band)=180x1.5(rain)=270)
If you decide to go the other way, it will be 654 atk with 90 power aqua jet