As I recall there were some questions about particular record types whose size had changed when we had staggered versions before. Is a CK 1.7 impending, and should one wait for it?

Using CK 1.6.89 on Skyrim 1.7.7 should be fine. It's only a Bat Thing™ if you're using a CK version that exceeds the game version.

That said, yes, there will need to be a CK update at some point due to changes in some of the internal records, especially with navmeshes in Dawnguard. So I'd caution against touching those for now.