Congratulations on your new bike! How has it been so far? I am 5'5" and tried both a 48 and a 51 - the 48 felt too cramped and the 51 was much more comfortable although I had less clearance over the top. I tried the SuperSix, albeit in a 51, and it was way too stretched out for me and I couldn't see it being comfortable for me in the long run. There were no 48s in the store for me to try but I ended up picking the 51 Synapse both for the overall comfort and yes, the color.

Here's hoping for many happy miles for you and your bike!