i'm 5'5" and a friend's 50cm was just a hair on the large side for me. remember that with a lot of these stock bikes, a 50cm has a 53cm top tube. the 47, with a 50cm top tube, will probably fit you better - but it's just speculation. however, i feel confident encouraging you to get the 47.
mercier lit doesn't say anything about the 47 having 650s. it probably has 700s.
you should consider getting 165mm cranks, if the bike comes with 170s. for short folks like us, 165s are beneficial.
saddles, saddle height, handlebar-and-stem setups - all these are personal and might take a little while to get to a comfortable position.