Hey Steven,
No i have not directly. But having looked at arnold videos on the net, with computer specs given, i can state that from what i have seen, arnold is close to mantra in terms of displacement speed (which i have used). So it is close to a reyes renderer in that sense. Again, this is comparing what i know to what i have seen (but you can't really cheat rendering speed). Vray is definitely not that fast.
