fruity,
I'm thinking there are a number of mulberries floating around out there that are called 'Pakistan' - whether or not they are the 'real' one, is another thing altogether.

IIRC, Mike McConkey at Edible Landscaping is the one who initially imported it.
According to Dr. AJ Bullard, the long-time NAFEX mulberry expert, in Islamabad, Pakistan, where it originated, the lowest recorded temperature is 28F. So... is it hardier than that? I don't know - but when I planted one, many years ago, I followed Dr. Bullard's recommendation and planted it with the graft union below ground level. It froze back to the ground 3 years in a row, but resprouted - and would grow 10 ft or more - but never fruited for me, here in southern west-central KY; so, I took it out.