I have a Bare Nex-Gen as well and use Expedition weight Polyrpo. Works fine in warmer climates (I've dove with it in up to 84*), and I wouldn't hesitate trying it in water down to the low 60's. I've only dove 1x in 50* water and I added a couple of wool sweaters to the polypro - was fine... might have been fine without the extra actually Nice thing about the NexGen suit is the socks are compressed neoprene, so you get some insulation from them.
Aloha, Tim
Aloha, Tim