Ah ok. I apologize for posting too fast. I will be sure to go further in exhausting all resources before I post in the future. However, I did find some of the descriptions of the iostreams parts and how they compose (especially examples, that's what I was really looking for) vague, IMHO.  

No, I haven't measured performance.

Those unnecessary allocation copies would, in the worst case, result in a 2-3x slowdown of the entire program

due to the fact that it's literally pausing to repeat something that's unnecessary. 

But actually, if this appends my 30k string, I didn't know it. The back_insert_device<string> object wasn't something that I understood very well from the description at http://www.boost.org/doc/libs/1_45_0/libs/iostreams/doc/classes/back_inserter.html

From what I had thought though, if my string was empty with 0's,

and I appended to it, then I would end up with precisely my compressed data. The idea of acquireStringFromPool is that it returns a large string that is always cleared out for the filtering_ostream to fill up as though it were a device. Is that incorrect? How can I get that functionality?

Perhaps, however, that reserve approach would be good. I apologize the email was so long lol.