The sizing charts you find online are really just guidelines - nothing can substitute for trying out the real thing, and the easiest way to do this is to visit your LBS and try them out. I'm 5'3" and have a 28-inch inseam, which I've discovered is closer to a man's proportions than a woman's (I have a longer torso and shorter legs). When I recently decided it was time to buy a road bike (I have been riding a Trek FX7.2), I thought I needed/wanted a WSD frame. Then, I actually tried out a few and found out quickly that although the standover worked, the top tube was way too short for me. I was also trying to find something on Craigslist/eBay but finally realized that I needed to be professionally fit. Ended up yesterday with a beautiful 49-inch 2008 LeMond Alpe d'Huez (Trek has discontinued the LeMond line so I saved 1/3 and it's way more bike than I ever expected to get.) I test rode a few other models, and all I can say is when you get on the right bike you will know it.

As for wasting the time of the folks at the LBS, you certainly are not wasting their time. A good bike is an investment and you need to make sure you have evaluated the possibilities! Eventually you will need your bike serviced no matter where you buy it, and "window shopping" will give you a good idea of how it will be to deal with various stores and their personnel.

Good luck and let us know what you end up with!