Go with the K1. You're looking for flow and the K1 has more of it.
However, if you're willing/able to spend the extra I suggest a Tunze nanostream. I have a 6045 and a Koralia 2 and the Tunze is more user friendly and much less obtrusive. It's easier to hide because it's round and the mount holds it closer to the glass and you have a limited range of motion with the Koralia.
I'm not dissatisfied with the Koralia... just more satisfied with the Tunze.