First off King Bettas are known for being more peaceful (from other people and my own expierience). Second they're not giant at all. Not even close.
Another thing is Betta Raja IS HUGE! I've seen them in person and they are seriously huge!
I will buy one soon sicne I have a huge PK female that will work for breeding to one. IDK if anyone has done it but it help us see exactly what's in their genes.
Who am I? Well I am a Junior Member of the International Betta Congress and a breeder of white HMPKs, red dragon HMPKs, black/red dragon HMPKs, metallic multi HMPKs, blue masked HMPKs, and now multi color HMs. Soon to add black HMs. I will be showing in New Breeder class in fall of 2012.