Unfortunately, since Reno backs off later than Vegas, a mixed Vegas/Reno network ends with the Reno machines consuming the vast majority of bandwidth.

Unless they're idle most of the time, that is. Anybody who's run a modern BitTorrent client alongside a web browser has been in this situation: the congestion control protocol used by most BitTorrent clients watches for packet delays and backs off before TCP, so it's much lower-priority than just about everything else. Even so, it can end up using the vast majority of bandwidth, because nobody else was using it.