Regarding the specific sexual act, there are many hard anal scenes in the LegalPorno catalogue (mostly because of extreme dilatations and long time stuffing).
If it comes to the general atmosphere, Cody Lane's infamous "Blue Room" scene is probably the hardest I know.
Veronica Leal's scene for HerLimit with Luca Ferrero is very rough too, as many classic scenes for the Kink network are (The Wife and the Servant, The Big Bust, The Dinner), with Truth or Dare (starring Jessie Rogers) standing out, partly because it shares a similar theme as the "Blue Room" scene.