Hi Klaus,
Welcome to the forum.
First, probably any of the boats you mention would sail
offshore. Not familiar with the Standfast and the BR43 would depend on who built the boat (most SA built BR seem to be well made). In general I think most sailors say Beneteaus are better made than Jenneaus.
Keel. I have owned boats with external lead keel bolted on and encapsulated keels. For a cruising boat I prefer the encapsulated design since it eliminates a few
maintenance concerns. With an external keel you do need to make sure the bolts are in good condition and I found that the joint between the keel and the
hull always worked a little and showed a thin line every time I hauled, even though I caulked and sealed it every time. Always made me wonder how much
salt water was seeping into the joint and corroding the
keel bolts where I couldn't see them.
All that being said, plenty of boats have external keels and sail for many years without a problem. If I found the perfect boat I would not scratch it from the list due the that one feature.