I started my apfelwein yesterday, a five gallon batch in a five gallon carboy, with about five inches of airspace, and already it is bubbling over. I am going to have to do what you did, and move it to a six gallon to prevent having a huge mess in my kitchen.
however, after much of the fermentation is over (at least the rapid part anyway) ill move it back to the five gallon. too much airspace makes your wine susceptible to oxidation and other nasty things. its better to just invest in one or two five gallon ones, especially if your going to keep making more.