some of them are pretty tough to solo even at 50, depends on you class. A party in the 30-40 range 5-8 people shuold be able to do it. Heres a tip for you: kill them in less then five mins or you will wait longer for pops. They pop every five mins 12:00, 12:05, 12:10 and so on. So if you kill one at 12:04 you only wait 1 min for pop, if you kill one at 12:06 you wait 4 mins.