Have you tried the 54? Your LBS can help determine which is better. If the 54 is a good fit except for reach (the seat isn't at it's lowest point), the stem can be changed. I'm surprised that the 52 comes with 650 wheels. Usually it's 48 or smaller bikes with 650 wheels. One thing to be wary of with smaller bikes and larger wheels is to overlap. That's where your toe can strike the wheel (or fender if you have fenders) when the wheel is turned. At 5'7" with 30" inseam (which is no the same as cycling seam, which I believe is floor to "anatomy"), I have this problem on both of my road bikes. I just live with it and am careful when I encounter a sharp turn. Being female and having a short reach, I found that 50-52 were the right sizes for me. But I never test rode any Salsas. YMMV.
If you are in between the two sizes, perhaps you should try some other brands of bikes which might fit a bit different and you fit one size better. You really need to ride BOTH bikes in order to decide. If you purchase a bike that is too big, you will not enjoy riding it. Fit trump "love" when it comes to purchasing a bike :-/