Re: @Jim Mitchell
Most recent open compute specs are moving towards 12VDC or 48VDC busbars. All the sensible folks are doing it.
Efficiency for DC/DC is in the very high 90, and also very small, look at some of the Analog Devices DC/DC modules and you can do 100A @ 1.2V from something quarter the size of a matchbox with 12V input.
Busbars are pretty easy, substantial but still not a problem. I've seen 100kW per rack prototype systems with 3x 48V busbars. There are EU funded supercomputer research projects pushing that level of density.