Tim O'Shea worked on improving latency within a GNU Radio flowgraph by being able to adjust the size of the buffers. He worked on looking at two features that will be worked into GNU Radio: the ability to set the maximum noutput_items and the ability to actually control the size of the buffers.
The results are mostly based on the latter and can be found here: https://github.com/osh/gr-latency/wiki/Initial-Results