Welcome to the forum.
It depends what you mean by extreme weather conditions. All 5m RIBs are ultimately limited by their size. That said - plenty examples of RIBs circumnavigating UK that fall into this class, including Harry Dywer in his (effectively rebuilt Avon 4.0m Searider) if you search on YouTube.
Anything to handle swell needs to have a deep V, so that should be on your list of priorities, probably jockey seat set up, hypalon tubeset, etc.
Not sure what the restrictions are for importing into Croatia - that will be based on your budget and local taxes. If it were me I'd include these in any search. I'm sure other forum members will add to this.
Ribcraft 4.8m - 75hp
Ribcraft 5.0m - 90hp
Avon Searider 4.7m (rare) - 5.6m
Ribquest 4.8m (pretty rare - but you never know)
Delta 5.5m