I like the idea of using the low voltage on a good quality fan, but as I mentioned

I do have the settings in the BIOS - it's just that they don't do anything.
Cheap case I know, but I don't want to get a 4 wire fan only to find that's not the answer. That was the - perhaps obscure - reason that I mentioned the HP. It varies the speed with only three wires.
I'll get back with the settings options