Ice---this past hunting season I was hunting in -28c temps with my 68 lb bow without a hitch.If you practice with it yearly and 70 lbs is comfortable to you then get it.
I will stand up and stretch once an hour and draw my bow back when it gets cold,just to loosen up my mussles.
Just set your bow at whatever poundage your comfy with between 60 to 70 lbs and keep it there,just remember,bows tend to shoot better at max poundage.