green gas is fine-ish in winter (it'll still wear the slide out eventually, but nothing is forever), you'll get horrible gas efficiency from it though. I recommend abbey predator ultra gas, powerful enough to make it work even in the dead of winter and it compresses much better than propane (green is propane+lube) so you get better gas efficiency too.
Green gas at higher temperatures (and thus higher pressure) will require you to install a 150% hammer-spring - they're about £10, but are a bit of a bitch to install - otherwise the valve knocker won't hit hard enough for the mag to expel gas.
brut is the same stuff as predator ultra but without the UPL lube mixed in. It's marginally more powerful as a result, but not excessively so, still weaker than green/propane.