Riding contra-flow is bad for two main reasons, IMO.
The first, is cars don't expect you. This requires you to be extra cautious at any crossing a car may come from.
Second, it increases the collision speed should an accident occur.

I'd feel comfortable riding contra flow given three requirements are met. There are few to no cross streets, traffic is moving far faster then 40mph, and there is a large paved shoulder.

If this was indeed a 4 lane highway, I'm guessing all those things are true. If cars are doing 50+ mph, a collision will likely kill you regardless which direction you're traveling.