The main function of your boot is to apply pressure to the front of your ski when you lean into it. Depending upon lots of factors like how stiff you ski is, where your bindings are mounted, how long your leg (lever) is, how fast you are skiing, what kind of snow you are on, etc. your boot may feel too soft or too stiff on any given turn. The bottom line (assuming that your skis are tuned properly) is how the front of your ski reacts when you lean into the boot. If you can make your skis hold an edge on hard snow at speed without too much effort, your boots are probably stiff enough. If you are applying forward pressure to your boots and it is not immediately getting to the front of your skis, then the boots are too soft.
With the new short shaped skis, you don't need as stiff a boot as with the old long straight skis. Also, intermedaite skis are made less torsionally stiff to initiate a turn more easily, hence they match better with a softer boot. A stiff boot will over-turn them and make them feel squirrley. Conversly, if you are stepping up to a stiffer ski, you may need a stiffer boot to drive it.
I prefer a somewhat softer boot with a progressive flex that lets me "hang forward" on it (more like a tele boot), but many people like a stiffer one that gives a sharper and more immediate response from their skis as soon as they lean just a little forward. If it feels to you like you have to throw yourself way forward in order to get a response from your skis, then your boots are probably too soft for your body and style of skiing.
One person's slipper is another person's rocket. Don't worry about the numbers, go by the feel and the performance.