Hi Flight Level Photography,
One key feature of the d7xxxvs vs d3xx is the Mode Dial (d7100 shown below).
With the d3xxx thru d7xxx you get a Mode Dial that allows automatic programing - see
Figure A.
From what I understand, unlike your d3100, the d300/d300s do not have automatic programing. Notice the difference in
Figure B. You have are three buttons for controlling your WB, ISO and QUAL.
FWIW
Cheers