Comparing the stiffness of one boot to another is an inexact science, and there's no definitive scale. Most companies have their own flex scales, and while sometimes they're roughly comparable — Nordica's Dobermann Pro 130, for instance, is a notch stiffer than the Lange Comp 120 — more often they aren't. The only reliable way to gauge a boot's flex is to try it on. If you want to compare models, try one on each foot. And remember, what feels too soft in a warm ski shop might be perfect in cold weather.
Gear Question: Boot Flex