Well there was no need to do the test, because if you kept the same shading rate then of course the double size render was better. I could have told you that without even trying. Why wouldn't it be? Since you effectively increased the sampling rate by a factor of 4, because you didn't adjust it for the new size, this should be a much better, more detailed render, with less aliasing.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)