One-piece v2 gearboxes have a general design flaw across all brands. I've cracked Progear (Systema) "reinforced" v2 gearboxes while playing in the winter before.
The sig551 I may worry about because it's so plasticy... plastic becomes brittle when cold
The 552 should be okay, but you'll have to run an external battery pack, a mini won't cut it.
The M14 should be fine, the gearbox seems strong.
G36 and AK seem fine.
STOCK v2 gearbox guns should be okay as long as you keep dry firing to a minimum.
meuhey: regarding hop up, nobody said that keeping it on will damage it. Just that because the material becomes stiffer in the cold, you'll have to reduce your regular hop up setting on game day to compensate or your BBs will have too much backspin on it.