For anyone else in my position, who thought that AC won because it was inherently more efficient for transmission, the Wikipedia page [1] has a nice overview of HVDC. There's also this PDF from Siemens[2] with some data. Interesting points: the voltage being discussed is in the hundreds of thousands of volts (800,000 for the line in the PDF), and the transmission losses are apparently 30-50% lower for HVDC.

1. https://en.wikipedia.org/wiki/High-voltage_direct_current

2. https://www.siemens.com/press/pool/de/events/2012/energy/201...