Some comp safari/ultra4 cars have more money in their shocks than most of us have in their entire car, so I'd say we shouldn't waste too much time looking at these. Anyway, from how I understand suspension for going fast in the most simplistic way is this:
You need to aim for the softest spring you can possibly fit without the wheel hitting the bump stops too often. And to do that the shocks are the main thing. So too high a damping rate will make it a bone shaker. So dampers have a variable damping rate. To achieve this, there are 2 options:
A bypass damper, which makes the damper rate higher the further it moves up the stroke. These are being used for baja and ultra 4, and in recent years also getting used in comp safari.
The other option is different damper rates for different speeds. So dampers that have adjusters for high speed and low speed. These are used in WRC and Dakar.
I am not sure why the different approaches are used in different disciplines. I think a big problem with the setup on ultra 4 etc, is 3 dampers per wheel: so there is a coilover, a bypass and the hydraulic bumpstop. So you have 12 dampers on the car. Where as WRC have everything, including the bump stop built in a single damper, so you only have 4 dampers on the car. Dakar cars have usually 2 dampers per corner.
The tricky bit is setting them up. the dampers can be rebuild and revalved to make the car handle the way you like. To do this you need to go testing and try several different valvings and springs untill it behaves the way you want. Ideally, you need to get a couple of sets of dampers, so you can test while your shock technician revalves another set, than swap over. When I mention a shock technician, we probably start to think it gets a bit involved. So once you have spend a load of money on the actual shocks, you are going to spend even more money on getting them dialled in properly. Here is were we just cannot keep up with big spenders basically.
Interestingly, In a tuning guide for fox shocks, they stated that they make many more shocks than they make valving sets, so the majority just fits them out of the box and call it done, never really get the full benefit.
Anyway, back to the level were most of us operate, I have never got too far into dampers myself, but Fox does the truck & SUV range, which allows their dampers to be used as a direct fit to your car. There is this one, called the IFP which has no external reservoir:
Or this one with external reservoir and adjuster:
I had an adjustable set at the front, and the IFPs at the back for croatia. (Prolinx only had 2 external reservoir versions in stock at the time) And they were a different league from the old man emus I had previously. So that is my recommendation. even just fitting the IFPs will be a big improvement over any mass production damper. And at that price, i'd say it is the best bang for buck you are ever going to get for your suspension.
I don't think a bypass damper has much to offer on a defender, as it is not a good fit at the front, but the high speed/low speed adjustment approach is certainly a good thing to have.
There are problems though,as the the pin fixings have very stiff rubbers. I didn't dare to do them up fully, which resulted in 1 damper loosing its rubbers somewhere on the M40. So Then I did do them up as tight as possible. This resulted in the shafts bending under full articulation. So although I recommend them, I would replace the bottom pin fixings for rodends at the bottom.
When we have are soft springs, cornering gets interesting, so an anti roll bar can be used, but this makes setting up harder again as the roll bar also influences wheel movement at speed. Also for cornering, castor is good for steering feel and it means your wheel will roll on camber in corners, which is good to get it to turn in.
Anyway, from my little knowledge of suspension.