I always do 40 along there and 50 in the bit further along, simply because I know they have regular patrols along there (I know that NOW!

), and the amount of drivers that swerve out late because they are going much faster and come close to taking me out, or give me headlight flashes, or give me the finger as they overtake simply because I am going at the speed limit is quite frightening.
I genuinely think 40 is a dangerously low speed for part of that section. Nearer the motorway roundabout I could agree with it due to the queues. (The typical lets lower the speed limit rather than sort out the congestion issue, but hey ho!)
I am actually quite surprised that they haven't lobbed Specs cameras along it by now...