I agree with **dlfurman. ** Different scene settings demand unique render settings to optimize your lighting balance and texture requirements.  There are many variables to consider, but those settings optimized to the max are not necessarily the best for your computer set up.  There will be compromises which will determine how long you are willing to patiently wait for a render to finish.  It is not unheard of having renders run through the night and then some.  Experiment  and see what works for you.