As I haven't tested it with groups that size, it would be interesting to hear how it goes! The main thing I'd expect is players tag-teaming a lot during combat, which might make fights against single opponents (e.g. greater foes) trivial and could get repetitive. I might suggest trying out some area of effect attacks which keep players on their toes. Other than that, I'd think about boosting the hit tolerance of enemies by a few points. Hope it goes well, and enjoy!