When I had the Nikon D3 the outer points didn't work well for me in low light. In very low light I couldn't lock focus with the D3 but my Canon 40D would lock focus on the outer points. I ended up using only the center AF point on the D3 most of the time. In dim restaurants I'd often use outer points on the 40D but with the D3 I'd just use the center.
The Canon 5D2 is worse than those two and I only use the center point in low light, but with more light I might use the outer points, like outdoors when it's bright.
The Mamiya AFD2 needs a bunch of light to focus. With tight DOF my biggest problem is the movement of subjects. They tend to wobble some while I recompose.
It's an interesting question whether the D3x has exactly the same focus function as the D3; my finder is off-center - the screen, not the frame.