You may find a 50cm cross bike frame to be too small. I have a 50cm Bianchi Castro Valley (same geometry I think as their Volpe). I am 5'6" on a good day with a relatively short inseam - probably about 3" less than yours. The 50cm fits me fine, note I've never used tires bigger than 35mm studded on it. Or at least you will have plenty of seat post showing - useful for mounting large saddlebags. A longer stem can help some with handlebar reach, but it'll still be a compromise. I'd keep looking for a frame that is the correct size, unless you need to build that bike NOW.

45mm tires are pretty big - do you really need something that wide?