"Heavenly Bamboo" is just a common name for all nandinas. 'Firepower', is a specific cultivar. Most of PA should be more like zone 6 than 5b, these days. I'll bet they'd do fine there (possibly remaining evergreen, possibly as a dieback shrub), but you could check with a local reputable nursery for first hand experience in your area. Dirr mentions them growing in "southern Connecticut, Cape Cod, Cincinnati, and Louisville."