I'm trying to resurrect this thread as I have a similar question. I'm travelling on BA in J next week and am trying to avoid checking luggage as I have a tight connection at my final destination which is an unfamiliar airport (FCO) and which is on a different ticket (don't ask).

What are the odds I could get away with a roller carry-on, laptop bag, and a garment bag? Aircraft will be a 747 then a 321.