I'm 5'4" with longish legs just like you. I had the 15" Trek wsd fx and went to the 17.5" regular Trek fx the second time. There is no difference in the geometry of the wsd and the regular 7.2fx. It changes as you go up the fx line though. I showed a printout of the geometry to my lbs and they were surprised too. The 17" was a better fit for me, so maybe you just need to get used to it. Also, I don't do the lycra only and I've been riding a long time. What I do is wear good padded shorts under a pair of regular shorts or capris, like mountain biking style or wear a Terry wrap skirt. I do recreational rides that are always more than 30 miles and they work beautifully.

Congratulations and have fun!