Ekok Mamfe road (Cameroon) in july will be ALOT of fun but slow going...its a pretty poor road. In the rains its a muddy mess, with huge holes big enough to swallow the truck. They say this area of Cameroon aroud here and Korup nat park has the 3rd highest rainfall in the world? Not sure thats correct but somebody read that to me.
An alternative is to enter the north of cameroon near Maroua or Mora (sorry forget the name). The raad south to Ngoundere is potholed tar though they are working on it in places (Lagdo Bleu def worth a stop for a night).
The road then to Foumban from Ngoundere is mostly dirt, with some new tar to help you get up and down the hills.....but if it rains, that road will be pretty bad in places. Some big holes too, but the road is geneally wider so you can avoid them. On Ekok Mamfe the road is right through the jungle at times so not easy to avoid the holes with a bigger vehicle.
I saw a UK biker who said he crossed into Cameroon from Nigeria about half way up the countrys borders, but that you could only do it in a bike, a bigger vehicle would find it impossible. Not sure if thats true, just word of mouth
Cameroons roads are definitely more testing to drive on in terms of conditions (esp in the rain), but Nigeria is worse for crazy drivers...watch out for those bikes, esp around Abeoukouta, Kano, Lagos, Akure, Enugu etc!