A universal joint does not operate at a constant velocity as it goes through its arc of movement. This situation is improved if there is a UJ at each end of the shaft, but it still gives changes in angular velocity at the extremes of articulation that are required on the steered end of the car.
As the name suggests, a Constant Velocity joint is designed to give a constant velocity during angular articulation, but as MattR notes above, there are extremes when it can't continue to give that. There's a reason for that - it isn't really a CV joint! It's a clever adaption of the designs in the attached link. As you can see, a true CV joint is the one with the spherical cages trapping six balls. This would be too expensive and difficult to make in our sized cars.
http://en.wikipedia.org/wiki/Constant_velocity_joint
As for the handling impacts, it is likely that the UJ will help with traction as action of the joint will tend to drive the wheel into the track. However, as it isn't a constant velocity I would expect that it would give you problems on large jumps and bumps where the car may land with differing rear wheel velocities. The so-called CV joint most people use removes many of these issues, and should give a much more linear response in all situations.
At the front, the likelihood is that a UJ will drive the wheel at variable velocities during cornering and give some darting effect. At high speed and a bit of lock, the UJ will tend to pull the wheel straight making high-speed steering a bit of a struggle.
That's all theory, you need a top-ten driver to tell you the practice! HTH
