Vespaio is authentic and romantic, but they still didn't take reservations when I was there fairly recently. They will take your phone # and call you when your table is ready (expect at least an hour wait on weekends), so you can walk up South Congress Ave. while you wait. My date and I stopped in Guero's (Tex-Mex, btw) for a drink while we waited for the call. FWIW, the bar at Vespaio was also packed -- Guero's was crowded, but we were able to sit at the bar. Vespaio is a little close-quartered, but you can probably have an intimate conversation if your voice doesn't carry (mine does -- lol).
North serves decent Italian -- it's in the Domain, which is a trendy outdoor mall in north Austin. They take reservations, but it's very close-quartered, and it's practically impossible to talk privately. Has anybody been to the new place in the Domain, btw? I'm blanking on the name, but it's also Italian (I think).
Trio in the Four Seasons is upscale American -- I've been there a few times. They take reservations. You can definitely have an intimate conversation there. A little pricey, but not too bad. I've found the waitstaff to be a little inept -- you would expect better from the 4 Seasons -- but tolerable, and friendly. Be sure to get the rosemary steak fries -- yummy. After dinner, you can go upstairs to the lounge for dessert, before you have the provider for dessert
Chicks dig the Four Seasons
Good luck!