Core idea of this stuff is to run compact_buffer when idle, e.g. with:

(defun idle-compact-buffers (timeout)
   (run-with-idle-timer
    timeout t
    '(lambda nil
       (mapcar '(lambda (buffer)
                  (if (not (eq buffer (current-buffer)))
                      (compact-buffer buffer)))
               (buffer-list)))))

This offloads Fgarbage_collect, especially if there are a few hundreds of buffers.

Dmitry