Violent is the point-- shutdown might be prohibitively slow. Or it'll get stuck waiting to umount a network share. Or maybe, you want the DRAMs to go dark and start losing ASAP, I don't know. If you must, simply precede 'o' with some sequence of 's', 'e', 'u' so it'll go down hard and fast, but still a bit controlled. I find that 'u' succeeds more often if done after 'e'.

FWIW, this is just what I do with the keyboard (but more slowly) when something went wrong enough that I can't even switch to a text VT and recover. Sometimes even 'b' won't hard reset it-- which indicates everything was already hosed, or maybe just the keyboard. Presumably the umount didn't work either, but I gave it a chance.