stay foward = no more shin bang
Some people may take exception to this but, shin bang really has nothing to do with the flex of a boot. You get shin bang from leaning back when you ski, or landing in the backseat. It makes no difference if your boot flex rating is 60 or 150 when shin bang is your issue. A stiffer boot does a better job of transfering energy to the tips of skis efficiently. That's how you used to get skis with minimal sidecut arced and carving. That's why very stiff boots are less important now, because with these big sidecuts, weighting tips is less important. You need a lateraly stiff boot so you can simply tip the ski on edge and carve. Most people who still prefer stiff flexes (120+) probably like to ski over the tips of their skis rather than centered, or have bad bone spurs on their heels and get they punished when they flex through softer boots.