Ok, so I spent the afternoon with a repair specialist and distributor for these tripod manufacturers. Get this, he is all alone and in an obscure industrial park in the suburbs of Paris. There is a commercial representative somewhere on the French coast. That's it. This is what has become of this industry for an entire country. That is what the internet has done for commercialization and distribution. Here is what I found out from this very helpful fellow, who obviously wanted to share his knowledge with someone who cared enough to listen:
Sachtler, Vinten and Bogen/Manfrotto (for tripods) are all the same company.
Previous to this Sachtler and Vinten only produced high end, expensive products. There was no entry level products. This is why Bogen/Manfrotto was purchased. To fill that gap.
Vinten Protouch and Vinten series 5 fluid head tripods are nothing more than rebranded Bogen/Manfrotto. Same manufacturer behind, same level of quality. Entry level. These are all friction based tripods. There are essentially two plastic disks with some oil that open and close around a column in order to create resistance. These are in the 700-800 USD range. Same level of quality as the 501/503/504 series from Bogen. Continuous drag fluid heads. Cartoni does the same on the cheap end of their product line. It's all pretty much the same. Friction and lot's of plastic, my friends.
Sachtler and Vinten use spring/shock absorber-like pieces of rubber in order to create resistance and give incremental differences in their more serious offerings. This is why they have solid incremental drag and are well damped. You will get a very well controlled pan or tilt with them as opposed to a friction head.
Now some important facts.
The Sachtler FSB series is really the same head (or shell) for almost all it's models.
What's the difference betwen the FSB 6 and the FSB 8? The FSB 6 has two springs/shock absorbers each for Tilt and Drag, the FSB 8 has three.
That's it. This is what you are paying for in the difference of price. An extra set of springs.
This is why the "6" has 3 incremental drag settings and the "8" has 5 settings.
This is also why the FSB 8 can hold more weight.
What this also means is that the lowest possible weight that both of these fluid heads can hold is exactly the same. Which is why it makes more sense to own the FSB 8. Greater range of weight capacity and therefore future proofing. It is only heavier by 300 grams.
Now the bad news.
Even though Sachtler says the 6 and the 8 can hold a minimum of 1kg, it is not true. They have bounceback with a typical DSLR and a small lens (about 1.3kg) They really don't start to function well for tilts until about 2kg in fact.
For mounting a simple DSLR with only a small lens (like a C/Y Zeiss 50/1.4) the minimum Tilt setting on these Sachtler's is 1 and it is not enough. When you tilt downwards to get that shot of those ants and when you tilt it all the way upwards for the airplane flying over head, it should not budge wherever you put it - it should not bounce back because of its springs and it should not fall if you let go. It should stay exactly where it is. If your camera is too light for the fluid head, there will be bounce back until your camera has either a heavier lens or more mass around it. In the case of these Sachtler heads and a superlight bare-bones DSLR setup, this is with the camera plate almost fully advanced forward on the tripod head.
Important: The only Sachler quick release system which works with a bare bones DSLR is the sideloading version. The Touch-n-Go quick release system (which should ideally be for us) will not work with a bare bones DSLR on the FSB 6 or 8. The plate cannot advance far enough forward for those of us who want to only work with a DSLR body and a small lens.
Guess how many springs the FSB 4 has?
So yes it will work with your body on the light end without bounce back, but don't plan on using more than 4kg when you decide to buy that new Redrock or Zacuto offering.
The problem with any non friction spring system is that it can only provide a limited range of tilt based on the fact that it has a physical object to limit it. (ie. a spring) Thus you can have your range at the light end, in the middle, or at the heavy end. But you can't have it all folks.
This means that your choice of tripod really must be based on how you work. Do you work simply with only the camera and a few lenses, or do you have a big rig and a lot of peripherals?
So, if you only work lightly get a Sachtler FSB 4. It costs only slightly more than a Bogen or another friction system and is way better damped and it's range is from 0 - 4kg.
If you tend to work with heavier rigs the FSB 8 head is the way to go as the greater range (2-9 Kg) is an investment for the future. It is only at this point that the Touch-n-Go release system is viable.
One of the few advantages of the FSB 6 (2- 6 kg) is that you can get Carbon Fiber legs in a very cheap package. This is the only real selling point of that head. It has nothing to do with the head at all. This package is not available for the FSB 8.
What we really want is a well damped fluid head with springs and a 0.5 -9.0 kg range to cover all our needs. Actually Sachtler supposedly just came out with it by revising their 18 and 20 heads (now called the 18 or 20 "S1"). It only costs $6000 ! These were supposed to have been modified for DSLR's. What is their minimum weight? 2kg. Same old dilemma.
As for Vinten, well if you have a 50 pound camera, who do you think I might recommend? Big and heavy, they don't mess around. We'll speak again about that when you buy your fully configured RED system.