If their converted earlier, as other people have said, its unlikely to make them more peaceful and as Redbeard says could make them more organised attackers. Another point is who converts them? Even presuming no other parties, such as Jews or Muslims as occurred in Rus, might Sweden at least go Orthodox rather than Catholic. Since they have strong trading and cultural contacts with both the Rus state and via it Byzantium. Also, for much of this period Byzantium and the Orthodox region was expanding and reasonably successful while the Catholic world continued to be plagued by external attacks and internal splits so the former might appear a far more suitable model for a would be converting monarch.
Steve