The aggressiveness scale is great, but doesn't tell you the whole story. A firecracker and a 100 watt lightbulb might give off the same amount of energy over their useful lives, but it's not the same (I don't know that that is true, btw, it
is just an example).
#9 is an older product, #82 is a newer product. #82 will give better results; it will hold its cut and be effective a little longer. Both of those are really, really mild.
#80 is a good product for minor marring; it is easy to use and breaks down in a nice gentle curve, leaving a large "time window" within which you can stop polishing and still have great results.
I wish I knew how to draw and post graphs and such. This is actually fascinating stuff. One of the problems with #83 that makes it hard to use is that it breaks down almost linearly. What that means in practical terms is that if you stop too soon OR too late you will get marring (from either the product not breaking down enough or from the pad scuffing the finish). That also makes the product-to-area-worked ratio important; the product has to be broken down completely before the product is dry. If you use the wrong amount, or try to work too large an area, then the product will be ineffective.
Sorry to sidetrack this to #83, but it's such a great example. #80 was developed after #83, and it is much easier to use.
Tom