(excerpts from my search for the heaviest metal song ever - recommendations are welcome)
Black Fangs (2011)
What's the optimum BPM required to achieve the optimum level of heavy? Ain't got a clue, but I tend to favor something between downright plodding and pleasingly mid-tempo. A super-low bass bottom that sounds like its rising up from the bowels of the earth helps the proceedings along and of course a simple yet effective riff.
All of which are present in Holy Transfusion, from Sourvein's Black Fangs (2011) album, their third full-length release over the course of about twenty years. I hadn't heard of them before but that's no surprise since I've been out of the metal loop for a while.
(Jump to 17:33 on the video)