I didn't lvl in party, since my brother change character (again) but as i remember pt mkill is always x5 only, solo is way faster if u got gear to solo ofc. Me and my brother start as int healers, he pull 3mobs i pulled 3 he did aoe i did mine he aoe heal and than i did same, another his and mine aoe and we pull next 6mobs, it was faster than solo. All depends on party setup, if in pt it's only you who did dmg than fk this go solo.