Before you ask, yes it is possible I have tested this on the radeon settings thing and it does say crossfire is enabled. Also yes it probably a silly thing to do but I do not care, I live on the edge.
From my own research, I've seen many different answers ranging from 550w to 850w. So I'd really like a solid answer. I don't want to worry about having too little, but I also don't want to get something overkill and spend more money than necessary.