It sounds to me like you're going to have to prioritize the top tube measurement (shorter) and the seat tube angle (slacker, 73 not 74/75). This may mean that you end up with a frame size (seat tube length) that seems smaller than what you might expect given your inseam. Note that in the Terry Isis/Symmetry, the smallest sizes get the classic 73 angle by using the two wheel sizes. (That's the "miracle" of the Terry geometry.) The middle sizes then have to get steeper (74), and then the largest sizes get back to 73. That's considerably slacker than most WSD designs, which typically have seat tube angles exceeding 73 in all sizes.

I definitely understand the reluctance to buy used, especially without the opportunity to extensively test-ride. However, keep in mind that if the used price you pay is reasonable, it's not difficult to resell for close to that price if you make a mistake. When I had to unload my used Bianchi that didn't fit properly, I got 90% of my purchase price back, within one day, by selling it on Craigslist. I've also sold bikes from a distance, and it's not that much of a hassle if you require that the buyer pay for professional boxing and shipping by your LBS.