Should I implement this as a Sink or an OutputFilter with boost::iostreams?

Question

I use a boost::iostreams::filtering_ostream to write debug logs for my application. I want to improve my debug logging by keeping the last 100 or so entries and saving them to a file in the event of a crash.

I imagine I can do this in two ways:

1. I can implement an OutputFilter that is a "no-op" on the stream data but keeps a limited list of the entries in some member variable.
2. I can implement a Sink that does something similar.

I see two advantages to option 1: I do not need to "tee" the stream to two destinations and there is a convenient basic_line_filter base-class that makes its implementation quite easy. But conceptually option 2 seems more correct. What other wisdom am I missing? What do you recommend? Is there a third/fourth way?