One example I can think of to distinguish between them would be from Shadowrun, with the street samurai who had wired reflexes installed on the cheap. The character reacts to things in a very jumpy way, like a tic on crack. This is helpful for when they need to do something quickly before another character (e.g. draw a pistol), but a hinderance for things where careful control is more important (e.g. a precise sniper shot). Surgery (the old-fashioned type which uses scalpels), lockpicking, tight-rope walking, golf, etc, are COO. Quick drawing pistols, drag racing, hitting buzzers on game shows, hockey goaltending, playing Sonic, etc, use REF. I guess it isn't always clear-cut (I can see Free Fall being COO, for instance), but I do think they are distuinguishable.