I commute on a 2001 Volpe gone road RD and cassette (12-25) and have ridden many Poprads.
The Poprad frame is lighter and stiffer - I've only ridden the 853 models.
The Volpe's 520 frame has a really nice ride though. The Poprad was very strange with 853 and Sora in the early 00's, everyone was swapping the Sora out. Now that it's 105 it makes a great package.

Bottom line: ride them both, look at pricing, go with your gut, but if you were to race, you'd have to swap out the triple if Volpe, but Poprad is already there. ... Volpe if loaded touring. I don't know if the newer Poprad has rack braze-ons.