Lets say kingdom X has 400m gc more than kingdom Y (I have no idea the GC spreads here btw) Kingdom Y will even this closer exchanging stealth for gc. There is ofcourse opportunity cost to that stealth use, but might as well use your gold to do the most damage at start. So most damage with a wave is emerald, send, wave, sapphire.
Or you can option 2 The Flogger
Send gold drake, watch them bleed out money never wave till fort is gone.
I like the emerald wave sapphire for someone that is vulturing a kd, especially when that kd explored more acres. More time to not be ready and more acres to take.
(Side note, I know this was horribly written my mind was all over the place)