Tech is a little lower in my intended new home. Income may take a hit but is not a factor. Holdings are pretty good, but the big factor is they are surely less developed than my current holdings - my goal is to increase troop strength in my kingdom. My counties have all holding slots filled, and everything is developed pretty much as far as tech will allow. AI controlled provinces don't develop nearly as well, overlords don't seem to develop their vassals' holdings, instead they hoard the money or spend it on shit like feasts and fabricated claims.
I can't develop holdings in counties I don't own, can't take over vassal's counties without upsetting a LOT of folks, and building new holdings in other people's counties is a tricky business (demesne limit + vassal opinion). So I figured conquering an emirate and taking it over, handing over my fully developed duchy to a doge, and spending my income maxing out the new counties is the way to go long term. My big concern is of course will there be problems from having my capitol outside my de jure kingdom?