I did a lot of experimenting and used to start at the highest quality all the time. As I started adding more to each setup, I found that if I start at draft and then work my way up, I could judge the real difference in quality.
My longest render was the pic "Wet Kiss" which took about 4 hours. I thought
Poser was locking up each time I tried to render. I finally let it go and when I got home at lunch, it was done. The most complex was the "PF 3rd Anniversary Party" (both pics in the gallery) The party pic had so many elements, that I had to figure out how many characters I could put into the building and still render. Then each render was imported as a background picture and more elements added. I did this several times to get the final result and had to balance quality vs. speed vs. what I wanted to achieve.
I think one of my misconceptions early on was that a high end machine would make anything fast. To an extent it does. As I gained more experience, what I have learned is that I have to balance the speed of the machine against the capabilities of the program.
Poser 6 is a good program with features that other programs doesn't have. It is a bit clunky, though, compared to others. But complex, high quality renders will take time no matter what program is used. I know an artist using radiosity settings in another program and the render took 156 hours. I think only a full sized render farm could have done better!