Stand development, if at all, makes only sense with a surface, or acutance developer, as opposed to a solvent developer, like D76. If you dilute D76 1+3, it partly loses the solvent action, so if you REALLY want to try it this way, dilute it, and make a test roll with HP5+ at various exposures, and then stand develop for, say 1 hour, and see what comes out. I am not sure you can dilute D76 much more, because this developer is not terribly active, so you might end up with insufficient amount of it to actually develop completely the film, even in 1 hour. You have to test it.
On a more sober note, if you want more speed or higher sharpness, why not try other developers? SPUR is making some that seem to be interesting.