FWIW, I ride a 54 Kona Major Jake and am a 54 in road bikes. My 54 Major Jake rides much bigger than any 54 road bike I have ridden. It rides more like a 55 or 56. That said, I love the bigger size. It touches my nads when I standover the top tub, but this has in no way affected my ability to ride it off road and only makes it nicer to ride on the road. For me, the longer length of the top tube is really nice.
Do you know your road bike size?