Just some thoughts from someone similar in height to you - but you didn't mention your inseam...
I am 5'2 and a half" with a 28" inseam and have one road bike that is is a 44.5 cm size (Terry Isis) and one that is a 46 cm size (Aegis Swift). The top tubes are virtually identical on the two bikes, but the Aegis has the longer seat tube so the standover is higher and doesn't actually have as much standover as I really should have; the Terry is better in that regard. I felt "immediately comfortable" on both bikes and also continued to feel comfortable after many miles, including centuries. I never started to feel that either bike was too small, although I did decide that both should have longer stems than the short stems they came with (6.5 cm on the Terry, 7 cm on the Aegis). There is plenty of wiggle room to lengthen those stems, and thus make the bikes bigger in the cockpit. I did actually change the Aegis stem to 9 cm, which ended up being perfect.
I test rode a Trek 5200 WSD in 47 cm and felt a little too stretched out, and there was no way to bring the bars up any higher, and I didn't want to shorten the stem. A 48 cm would definitely not work for me; it would be too long in the top tube. A lot of it depends on flexibility and how much of an angle you are able to make with your back and pelvis comfortably.
Make sure on the larger bikes that your elbows are soft when you're on the hoods. You arms should not be straight out with locked elbows, as you probably know. One difference for me was whether I could ride comfortably in the drops. I can do that very easily on both the bikes I mention but felt too stretched out (and low) in the drops on the 47 cm Trek. I like riding in the drops and think that any bike where the drops feel like too long a reach is probably too big.
On the smaller bikes, as I am sure the LBS folks told you, make sure your knee is not in front of the pedal spindle. If you put the saddle back on the rails and your knees are still in front of the pedal spindle, then the frame is too small. Because of your femur length, you might have a problem with that. If you can get your knee directly above the pedal spindle and still feel good on the bike, I'd personally go with the smaller bike. The smaller frame will weigh slightly less too, always a plus!
There always seems to be a tendency among male fitters to try to fit females on bikes with longer top tubes than are optimal, I think. What will work for a man won't necessarily work for a woman. I also think how you "feel" is probably more important than how you "look" (to the fitters). You need to be comfortable in your chosen posture on the bike. They are right that as you ride a road bike, you will probably find that you gain comfort in a slightly more aerodynamic position, but unless you plan to race, you may still end up in a more upright position than they would.
Good luck with your decision. You are doing the right thing by taking all the test rides. Let us know what you decide on!
Emily
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow