I'm 5'5", I tried a couple different bike models in 49cm, and although the bikes felt well underneath me, they also all felt awful, granted maybe a longer step would've helped.
But then I rode on a 52 and it was immensely more comfortable right off the bat, even if the bike doesn't feel as "under" me as the 49s do. I bought the 52 and couldn't be happier, the only change I needed was going from the stock 90mm stem to an 80mm stem (and honestly I could've kept the 90mm stem, 80 was more just preference). I never rode anything in 51, but I'd be curious to know how that felt.
In other words, I personally like being a tad more stretched out and didn't like the feel of a smaller bike.