I'd like to know if it is possible to "predict" or at least estimate the following parameters:
1. Render time for an HD resolution image - for instance, I know that a test render takes 20 minutes to complete. Is it possible to, basing on that value, construct some algorithm that will tell me the time required for a full HD render at twice the quality settings to complete?
2. The file size of the final HD resolution image - which is similar in principle. A 1024x576 test image is 1mb large - what will be the size of a 1920x1080 image then?
I know that twice as large means about four times the time it takes to render. I don't know about the quality settings. The only thing I can think of is doing small test renders and noting the difference between high and low quality settings, and from that you could predict the final rendering time. But maybe that's too simple logic.
According to the people at Pixel Plow, there is no satisfactory way to estimate a render time, since the whole thing cannot be considered "linear".
Image size and quality settings influence each other, probably similar to the saying "The whole is more than the sum of its parts". In addition, the available hardware certainly plays a role. So "test series" are most likely only meaningful for your own, or similar configurations.