[Rich A]

As Jason said,
Watts is the way to go.
My opinion Watts is better than IRS.
When a IRS car takes a turn the body/frame will roll and since the IRS unit is mounted directly into the body/frame it also rolls.
With the weight transfer from cornering and the body/frame/IRS unit rolls, the inside tire inherently wants to raise from the ground and causes loss of traction of the inside tire.
There are several way of correcting this kind of traction loss.
1.Adding suspension travel so that the tire doesn't loose contact with the ground when cornering.
2.Removing suspension travel by lowering vehicle.
3.Adding stiffer springs so that the suspension doesn't compress as much. This reduces roll and also causing a harsher ride.
4.Adding a swaybar, This reduces roll and also causing a harsher ride and DEFEATS the independant suspension.


5 Link (3link w/Watts)
The 5 link does several things.
The Watts link keeps the axle from moving from side to side(like a panhard bar but better).
The 5 link doesn't transfer minor road imperfection into the body/frame similar to the IRS suspension.
The Watts link keeps the axle housing horizontal with the ground and centered under the vehicle.
The Watts link doesn't transfer body/frame roll to the axle housing causing traction loss like the IRS suspension.
Meaning better handling.