Katrina,
Sorry it has taken me a bit to get back to answer your question.
I'm knee-deep in my busy writing season now, so that is taking first priority around our house.
As far as Write with the Best goes, the grammar portion comes in the opening days of each unit when the guide directs kiddos to find as many nouns, verbs, adjectives, and adverbs as possible in the provided writing passage. Since the provided passages all come from classic literature, you can imagine the number of each part of speech included in each passage!
It's so important to keep in mind that the WWTB directions specify that it is not necessary to find ALL of the examples of each part of speech in the passage, but rather to find "some" of each type instead.
There is an answer key provided, but if you go with the "some" rather than "all" mentality the exercise will go much better.
As far as Rod and Staff goes, I like kiddos to be beginning Rod and Staff English 4 or English 5, if possible, as they head into Write with the Best. This is what is scheduled in CTC grammar-wise (doing the level at half-speed and then finishing it the following year in RTR).
The Rod and Staff guideline is as much or more about the writing concepts and other English skills taught within that level, as it is about the grammar knowledge.
Blessings,
Carrie