A local fisherman had an Outback and a Revolution. He used the Outback for the lake and the Revolution for the ocean where he had to launch through mild surf.
They are both very stable -- the fisherman had only one leg and managed both boats well. The Outback is more stable on flat water but tends to bounce around more in a choppy sea (because of the flatter, wider hull). IMO between the two, the Revolution is the more seaworthy -- can handle wind and chop better and make better headway against an unfriendly sea. It's an excellent all around boat.
To answer your question more directly, I think the Outback would be great in flat water up to moderate chop where it will start to pound and bounce a bit. For open ocean I think it is also OK as long as the weather is reasonable.
Like reconlon, I personally like the Adventure best for bad weather if you think you may be caught in it. I don't think of it as unstable at all. Though you're not interested in speed, it does extend your range, comes in handy fighting currents and tides, and against sudden weather changes. It's a very smooth riding boat. The added length can be a problem for some people though (transport and storage).
Regardless of choice, I recommend the large rudder for maximum controlability and Turbofins for enhanced performance.
