55mpg combined would represent over a 15% increase over the current 47.5 combined, which I don't think is likely. In Honda's officially released video about the 2006 Civic Hybrid's new engine, they said it's 5% more efficient than the outgoing motor. That would put the new combined figure at about 50mpg combined. It's already now the start of the 2nd week of August and typically Honda releases all it's official specs and EPA figures on cars by no later than September, so we should know for certain very soon.