I'm interested in learning from the best and I take the assumption that 7th through 10th dans tend to be better at teaching than 1st through 4th.
That assumption is, in my opinion, flawed.
Just because someone is a high level practitioner
doesn't mean they are a high level teacher
. And just because someone has a reputation as a good teacher doesn't mean (s)he will be the best teacher for you. The teacher/student relationship in a martial art setting is something rather unique for westerners. It can be very personal and challenging. It is worth the time to find the teacher that you can connect with and learn the best from. And in general dan ranking has very little to do with that.
To quote an earlier post:
As for learning from the best...I always wonder when beginners say this. I want to learn to play tennis, and I've never picked up a racket -- should I seek out lessons from Roger Federer? That seems pointless, and maybe a little bit presumptuous. He's the greatest tennis player in the world, and I'm a rank beginner -- why would anyone think that I needed his instruction to learn tennis, or could benefit from it?