btw, Garrett, just to clarify Sonnon was not involved with Systema, per say under Vlad and Mikhail; but another similar system. They are similar and they aren't depending on where, who, and what the instructors were involved with in the Russian Mil. I see Sonnon's stretching as the russian stuff meets yoga. More than likely, Sonnon was familiar with yoga before the russian stuff or incorporated yogic elements into the russian body physical preparation.
If you have ever seen the Japanese calesthenics from their school system, it's very similar to Z-health and you'll see a lot of Japanese sensei do it in their various systems from karate to judo to kendo.
Pavel's stuff doesn't seem so RMA-like or yogic. There are very interesting stretches but I haven't seen anything that requires flowing body techniques. I think this has to do with the fact that Pavel isn't involved in RMA AFAIK.