I think the party is too large. I have 6 players including 2 paladins with high AC, an insane AC monk who can shut down anything with a grapple, a cleric, a ranger with healing spirits, and a wizard who focuses on evocation magic. The only time they've had any difficulty is when they split party and go totally reckless. The amount of healing available is ridiculous. There are 4 healers in a party of six. And this wasn't even done on purpose - it's just inherent in the design of the system.
As with 4e, too many healers definitely lowers the threat level.
The main thing with a powerful group is to have the monsters play to win; those with multi attack or in mobs should certainly CDG fallen PCs. And it's ok to have frequent Deadly+ encounters, as well as lots of encounters between LR.