Originally Posted by Skid
How do you know when you need to get stiffer/softer boots?
I think,all AFAIK...
Regarding Cassina's situation, I don't think your foot is supposed to move, nor your heel to lift, ever. That is not an issue of having outgrown a certain lower-end boot, but rather that those boots were ill-fitted for the feet in question in the first place. That said, this situation may not rear its ugly head until the liners have packed out.
So, the OP question:
You may need stiffer boots when edge-setting (pressuring the tongue) into a carve is too vague, or ineffective. In the extreme case, the boot may even kind of fold-over (not literally, but goes beyond the range where it provides some progressive resistance, to the point where it kinda capitulates). Aside from strength, weight, and aggression level, I think this is also ski-flex and surface (ice? hardpack?) dependent.
You may need softer boots when terrain irregularities transfers too much through the cuff and starts throwing you around. Again, this is also depend on all the prior-listed factors. This is of course assuming you are skiing correctly (forward or neutral) and not in the backseat, in which case you'll get thrown around anyways.
(Please correct me if I'm wrong, I definitely consider myself a noob in the defining of the mechanics of skiing.)