I've got a 2309 and just received my two additional 4GB RAM Cards. Put them in and I can say that the speed improved (now with 16GB). Not dramatically, however, some applications did always show the little rainbow disc when my Mac was "thinking". This is now gone.
I am on OS X 10.9.5 still and the whole Mac feels as if it can "breathe" more lightly with the additional RAM.