Oh, about the Flow...
Dave and I tested the NX2 SE which is the newer strap system. The AT still uses the old I Powerstrap.
In my opinion, it's worth the upgrade because as you mentioned, it'll be stiffer plus it has new tech. Flow is notoriously hard to set up and kick into. The NX2 completely solves these problems. Very easy to set up and thanks to the new highback system, you can kick in without an issue no matter how tight you like to set the caps.
I completely agree with Dave on the locking mechanism though. The rep was showing us his weird index and thumb flicking maneuver, but in practice didn't work out so well with a foot strapped in. Maybe they fixed that for the production model or it's something that gets easier over time.
The reason the footbeds look higher is because they are canted. I believe they are 2.5 degree cants.
As for your Missions, yes they are softer to you because of your size. I told Sabatoa when he was buying his new boots that they would be softer for him than the stated flex because of his size. He's freestyling in what's supposed to be stiff boots.
Guys like you two always have to subtract a couple points from flex ratings for bindings and boots. Unlike snowboards, bindings and boots aren't built for specific weight ranges.
I have to caution you though about Flows... they are not for everyone. People coming off traditional straps have more adjusting to do. The feel is almost completely different when riding Flows with Powercaps.
Where do you live? I have an old pair of Flows that I do not use. I might have all the screws for it I dunno. They are large in size and heavier than tanks. But I'd be happy to let you try them out just so you can get a feel for how Flow rides even though the newer models are light years ahead of the ones I own.
Consider the RS if you can get a good deal on it as well. It's their stiffest Powerstrap model: