The 400 series should be raised as the current 100km/hr bears no reality to the speeds people actually travel at.
One of the primary concerns has always been {and justifably so} having higher speed limits in the winter when snow/ice/visibility are genuine concerns. What they could do is have 120 during the spring/summer/fall and remain 100 during the winter months. Dec21 to March 21 which is officially winter would be a very easy time frame for people to remember. Certainly having electronic variable speed signs up would be ideal but also extremely costly having to put up electronic signs every km in the huge 400 series.