Stiffness (IMO): Targas -> CO2 -> Double Agent (stiffest)
I currently own a pair of 2011 Targas and 2010 Ride CADs (Double Agent predecessor), and owned a pair of CO2s last year. I ride my Targas on my all mountain board and the CADs on my freeride/pow board. The Targas are more of a mid-stiff binding, I can get a decent amount of play depending on which strap insert I have in. The highback is decently stiff and responsive as well. The CAD is MUCH stiffer all around than the Targa. The highback and ankle straps are exactly the same on the Double Agent, both of which are stiffer than the Targa. From my experience, the CO2 fits in between the Targa and CAD. A bit stiffer in both the straps and highback than the Targa, but not quite in CAD territory.
It's all subjective though, different people like different stiffness ratings for freeriding. Rider weight has a lot to do with it as well.