The King Inset is heavy, I was considering it until I discussed it with my custom builder and he did not see a performance advantage besides looks. Yes you do have a larger welding area but how much is really necessary. Can't wait to see it when it is done I am sure it will be beautiful.
I think you will like the King Inset. I just took delivery of a new Carl Strong steel frame built with Columbus Spirit that I had him use the Inset on as I liked the idea of using it with a fork designed for an Integrated Headset. He had to design a special headtube for it as standard Columbus steel headtube stock would not accomodate the larger cups in which the bearings are mounted. It has a very clean look. I'm just now building the bike so I can't tell you how it performs.....but it's a Chris King product so I don't think I'll be disappointed.