You're trying to be very specific here, and I appreciate that
, but you really can't be.
Polishing isn't a science, it's a skill, much like painting. You polish by eye and be feel, as opposed to by measurement.
Using the sisal and the black compound you can remove as much metal as you want. The more you polish, the more is removed. So the answer to your question, technically, is that any size scratches can be removed.
The trick, however, is that depending on the depth of the scratches, you might be better using a finer grade of sandpaper first, to save time with the black compound.
Obviously, if you work your way down from 320 to 1200 grit, you'll be saving yourself a lot of time with the black. However, if you just sand with 320, the black will still work (and will remove lots of metal) but it will take you much longer.
If you don't want to remove too much metal, and need to be sure about how much metal has been removed, there are many low tech and high tech measuring devices that will tell you how the thickness of the metal. This is really the only way to tell how much is removed....you can't tie it down to any average numbers because of all the factors previously mentioned.
That said, you aren't going to see big chunks of metal flying off the part when using the sisal and black combo....it's a gradual process.
If you want it to be an even more gradual process, step down to the brown compound, which contains less abrasive.
A question for you would be - how much metal is acceptable to lose?