Rings of Doom are indeed essential S&M gear. Mostly naked, with 2 rings of doom, that one [+0, -3] leather cap you found, and the [+0, -1] robe, a Whip of Slaughtering, and you are good to go.
I have successfully killed a PC after closing the gate with such a combination. Remember, as well as reducing your PV by 10, wearing two rings of doom will actually (wait for it) doom you, so some care is required.
/And when I say successfully, I mean accidentally.Grr.