I think the Vocabulary Strategies of Tune In to Interesting Words, Use Word Parts . . ., and Using Dictionaries (etc) are strategies that would still be important for these readers. I feel like I still grow with these, even as a proficient reader!
I would also think that many of comprehension strategies used with a variety of genres could be valuable for them to grow as readers. Gaining insights into author’s purposes for writing, questioning while reading, inferring and supporting with text evidences are a few that jump out at me that readers use throughout their reading lives.

I had several 6thgraders last year that were high readers and at first reporting -parent teacher meeting, three parents said their boys have really started to read - like decour books. They were pleased that their kids were reading more.
the choice part was a big factor and because they are older, I get them to be reading to self or a friend for up to 50 minutes in the morning (by mid Oct.). Then I can have two longer groups OR two groups and some individual conferring. Often with the high achievers, I did individual conferring and we would talk about their books and themselves as readers. I like the other persons ideas about authors purpose and techniques used as a writer too.
Marg

You might add some additional things to your menu. My current favorite supplemental content has come from Notice and Note by Kylene Beers and Robert Probst, and their newest book, Disrupting Thinking is really good, too.