Fuji NPZ 800 is one of my favourite films but I find it works best at 500 ISO - I haven't used the recently released variety as I have stocks of the old but I don't think there's much difference. At its rated 800 ISO I find it a bit underexposed. I also shoot low-light concerts and like yourself use 3200 b&w but also Fuji 1600 Press. Why not use this, it's rated at 1600 already and seems to holds its own at that speed.
CN III
