Ah, just remembered it. My first message in the Forum, some months ago, was about a strange happening: the estimate rendertime of my images was about the same with normal AA and Premium Settings. It happened again, and keep on happening. This last image, for example, gave me 4 hours estimate with normal AA (to which, you teach me, we have to add at least 50% for the last AA pass, so roughly about 6 hours). I rendered it with SoftShadows at 64rpp and the rendertime was 5 hours and 49 minutes. Frankly, I don't know why and, at this point, I couldn't care less: the shorter, the better... but the mystery remains. Puzzled Stefano