I have a Rimowa Topas (56x45x25) that is right on the limit for BA but I find it really useful and with some careful packing have done 10 day business trips in Asia with it. It fits in the E190s (just, sideways, and requires a bit of a push on the overhead - I had actually given the first time and asked for it to be put in the hold but the crew were adamant it was going to fit!). Similar to another poster's bag, it does get a bit heavy at times but the convenience and lack of effort to push it around is really worth it. They also make one 1 cm smaller at 55x45x25.