is it purely a 50/50 split? (given that both objects are the same construction.)

Yes.

The velocities of the two objects are relative only to each other. Their velocities relative to the ground are irrelevant.

Imagine they were floating in space when they collided. Then each object's velocity would be strictly a function of the velocity of the observer. That is, if you were traveling at the same speed (and direction, of course) as one of the objects, it would appear to you to be motionless, and the other object would appear to be traveling rapidly. If, instead, you travelled at the same speed and direction as the second object, then IT would appear to be motionless and the first object would appear to be the one traveling rapidly. Yet in each of these scenarios, the only thing that was different was the velocity of the observer, which could not have any effect on the outcome of the collision itself.

tanstaafl.