I've just finished reading Psychology of Violence - 'The Effect of Video Game Competition and Violence on Aggressive Behavior: Which Characteristic Has the Greatest Influence?' By Paul J. C. Adachi and Teena Willoughby, 2011.
It seems that there is more to video-game violence than just the violent content, it seems that the competitiveness of the actual video-game can also play a major role in increasing aggressive behaviour whether or not it is a violent or non-violent game. They tested around 60 psychology students to get these results but even they say that it isn't a big enough sample or a varied enough sample to represent a population. Despite this, the article/essay has managed to explain more about video-game rage (they would call it video-game aggression/violence) than anything I've read so far. However, it was very specific about certain variables and models in the research, and of course had technical jargon in which can mainly be understood by psychologists and psychology students, and therefore most of it was hard to understand (for me, that is).

Perhaps there may be a more generalised theory about video-game raging/aggression/violence somewhere, I'll just need to keep looking...