I found running full fellowship Skirms on my 5xRKs pretty hard. Especially when the slaves will select all the soldiers instead of the leader. But in a full fellow skirm, all mobs are sig/elite, so it takes time to kill them for not much XP. Best way i found wtih 5xRKs is to just 1 shot mobs on the run from quest location to quest location. IMO Skirms are shit multiboxing.