You guys won me over to ETTR

From what I've read, ISO 400 is basically the same as 200 in noise terms and can be less so if you take a scene that would work at 200 and overexpose it one stop at 400 (assuming clipping is controlled). You might gain by going to 800 and overexposing versus standard exposure at 400. Beyond that it becomes more debatable, and anyone who wants to can read the threads linked in the other messages here.