Inpd, The 49 cm frame also has 1 degree less HT angle for stability with the shorter wheelbase which could reflect the minor difference in ETT length. The head tube on the 54 cm frame is simply longer to attach the higher positioned top tube.

Looking at this another way, it'll take more spacers on the steering tube and a higher positioned seat post to make the 49 fit. I still feel the 54 cm frame is better, non binding advice. (I also wonder about any toe overlap with the smaller frame.)

Ultimately the decision is yours, good luck.

Brad