bb, thanks for your feedback.

This wasn't in any way intended as a scientific test.... I just wanted to do a direct comparison between the effectiveness of increasing the render size and reducing the shading rate, without changing anything else. 4x the area is why I tried a direct comparison with 0.25x the shading rate. Yes, I did think about it, even though I didn't mention it!

My result showed quite clearly that increasing the render size by a factor of 4 improved quality more effectively than decreasing the shading rate by a factor of 4, and also had little impact on render time. (I'd have to go back and time the renders to be absolutely sure about that claim, though).

This is a single test result and may be a generalisation, but it's one I'm willing to go along with for the moment.

Of course, we would combine the two controls, with the other settings as well, to give even better quality, at the expense of extra render time.

(edit) I was not using any postfilter.

OT: 
I had a terminal Poser Pro crash last night, and in the end I had to re-install the program. I'm still sorting out the SRs and the scripts and V4 stuff that were installed in my main Runtime. At least it's grey and raining outside, so I don't feel too bad about sitting here at my desk today!

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)