I would ask the shop to find a shorter seat post that will fit the Litespeed....you shouldn't be expected to buy it without riding it.

I agree with your shop guy that sizes can fluctuate somewhat between brands and models. See if he'll give you a range to consider.

As for WSD: I'm 5'4" with long legs and a short torso. By all accounts I should be the ideal WSD rider. But I have a preference for non-WSD bikes....go figure. I do keep an eye on things like handlebar width and brake and shift lever reach though. Ultimately, it's an individual decision, not some magic formula.

Good luck!