When the tv doens't fit it doesn't fit, and you have to exchange it for a smaller one. On the other hand, when it does fit, it is amazing how soon you get used to the size of a new tv. I remember we were shocked by the size of our new BV when it arrived to replace a 46" Samsung back in March. Now we consider it completely normal, if not a little too small. People say the 7-55 is very bulky, I only know the 11-55 which is much flatter, but I would think twice before exchanging it for a 10-46. Especially if you have to pay additional money.
Regarding the picture quality, from my point of view a modern 55" LCD outperforms every old crapy CRT by far. But you must migrate to digital reception, you can no longer use analogue cable, that looks awfull. So make sure a digital tuner is built into the BV10, that is a very expensive option for the BV10 and a major drawback against the BV11 where you only have to insert a smart card.