Boot Flex Rating System

So you've bought a new pair of eight pound skis and your  backcountry boots don't have enough backbone to push them around.  How do you figure out what boots would be more appropriate?

Interestingly, there is no universal standard for boot flex.  Some manufacturers assign their own rating system, but the ratings aren't useful for cross-brand comparisons.

Luckily, the folks over at Teton Gravity Research have already put together an unofficial rating system for the most popular boots.