As someone above mentioned, WSD is more about torso length than height. While I'm not 5'10'', I am 5'7'' which is taller than most women the WSD were built for. I can't ride unisex bikes, I guess because my arms are short...I don't know, I've always been told I have a long torso - but on unisex bikes my arms are way too stretched out and it is totally uncomfortable. Getting a WSD was like night and day. I ended up with a Giant Avail Advanced 2, and I LOVE it. I think it was a teeny bit longer in the top tube than the Specialized WSD bikes, so I definitely am not cramped, but I'm also not stretched out hanging on to the bars for dear life. The bike stores I shopped at all had XS, S, and M in stock. I fit on a S.

I did notice in shopping around that the Specialized WSD were very difficult to find in 54" and above - many were totally out of stock.

Anyway, it totally depends on your body geometry, but I happen to fit on WSD bikes, in the same size that a petite 5'2'' with long arms would fit on.