I forgot where I saw the article that put forward the argument about carb heat resulting in a more uniform burn. But the explanation given was, if I remember right, that the air/fuel mixture out of the carb was more uniform, and so each cylinder got pretty much the same mixture. The author could back the conclusion with FADEC temperature readings of each cylinder (more uniform when carb heat was applied.
On the comsumption issue I just though that a good way to find out exactly is to look up the engine performance tables vs. OAT at some given altitude.