On that Elixer/butter thought...the old polyweb coated strings were very slippery, the new Nanoweb coated strings have a slim coat that you dont even notice (well, barely) I string two of my guitars with Elixers (yes I sue different brands and types on each guitar).
My Prs has Elixer 9's
My Ibanez Baritone has Elixer Baritone strings (they are 12-60's I think...you may want to look into them for drop C tuning)
My Gibson has D'addario 10's
My Cort has D'addario 11's


I see you are playing a tremolo equipped guitar...bear in mind that down-tuning usually works best with stop tail/hard tail guitars...I have heard some stories about inconsistant tuning with down-tuned trem equipped guitars...