ps, the first drop bar bike my wife ever owned is a XS Giant Avail (43cm I think) from about 6 or 7 years ago. They even put on a shorter stem for her (a rather short one, probably 50 or 60mm) and it fit her really well.
What also helped her comfort is that the bars are a bit higher than the seat, which is completely doable on the LHT, but perhaps not on the trek 520.
attached is a screenshot of the geometry of her bike, I would at least suggest riding some xs bikes that you can find test rides on, and note the toptube length etc, to at least have a reference to both the lht and 520, which you arent allowed to ride or even sit on.
Her Giant toptube is said to be 51.5cm, the LHT 42cm EFFECTIVE TT is 505mm, the 46cm is 515--same as the Giant--but you may want a shorter stem.
So this appears to be in the ballpark.
this would be the most prudent way for you to have a real life idea of what X frame dimension feels like riding. And you could even take a tape measure and measure from seat post to front of drop bars of bikes you could ride, jot them down, and compare to the official specs of that bike. You could also measure the toptube, and again compare to what the surly and trek say their bikes dimensions are.
again, I feel the 26in wheel bike to be an advantage for shorter riders especially. I'm 5'10+ and one of my bikes is a 26in Surly with dropbars, and I like how I dont have toe overlap even with fenders and fat tires on. Nice in slow stuff.
26in wheels also result in slightly lower gearing, so a bit easier in first gear going up a hill with heavy bags.