Not sure if this helps, but I'm 176.5cm, I rode a Size M Propel with a 100mm stem and switched to a 56 Allez Sprint (also 100mm). I found the 56 Allez to be ever so slightly bigger than the M Propel. Just looking at the geometry for both at the respective websites, I'm going to say you probably will want to go with the 52 if the Propel fits right for you. Even at that, the reach is still going to be a little bit longer, and the stack is going to be a about 2cm shorter.
Are you just buying the frame and building it up, or are you buying the whole bike? If the latter, go to a shop and ride them both. Get them to swap out the stem on the 54 for the test ride. I will say, having switched from the Propel myself, the Allez is a bit more nimble bike. I wouldn't go so far as to say it's twitchy, but if you don't pay attention you can make some unintentional course changes until you get used to it.