I think it depends on the individual rig. More grunt you got -- the higher you can push them. No expert tho.
Quality versus frame rate, for some. (Jaggies versus stutter.)
Posting settings won't help, unless they are very similar systems. It's a fiddle with it deal. ATI/nVidia/AMD/Intel/vintage all make a difference. If you post your system spec's, maybe somebody will have some helpful info.
Imo; seat of the pants, trial and error, is the best approach. Might want to open notepad, or take a screenshot -- before you start 'fiddling'.
I max mine, with no loss in fps, and great seat of pants visuals.
Have you tried the Tweaker, available in the downloads section?