I run it at 60 after I'd done approximately 2/3 of the HFP quests (1paly 4 shaman) team. I would expect, given the nature of the boss fights, that you could do the same with 5 shaman.

The key for me was some strategy on a few of the pulls. This might help some:

Ramparts? Do I just suck 5 boxing?

Little different for you without a tank, but the basic strategies should be sound.