The differences are slight in bounce, but I believe the sole of the 54 is narrower. You may like that a little better from tighter lies assuming you dont have too much bounce for your short game style.

I might add that I have good luck from somewhat tight lies with the 54-11 bent to 55-12. The 56-11 would get bent to 55-10, which means it may not be nearly as effective in a soft bunker as a 55-12; would be great for hard-packed lies. I can hit a 58-12 from a tight fairway lie, but have to use a 60-07 in a hard pan bunker (they have a practice bunker at Adm Baker that is as hard as a rock).

A 54-11 bent to 55 would have a bounce of 12 degrees. A 56-11 bent to 55 would have a bounce of 10 degrees. I have a Spin-Milled 54-11 c-c bent to 55. I had it bent to 55 because 55-12 is what I am comfortable with and it works in most situations.