I have some experience with feral tank + 4 shamans, mainly from gearing up my shamans. First i tried 1 resto + 3 elemental, but found that resto shamans didn't have that much to do, so i changed to 4 elemental and it works very well and you blast through instances even with low gear. Ofc it is safer to spec 1 resto if your tank doesn't have good gear.

Atm i'm boxing with 2 mixed groups, first group has 1 elemental and 2 elementals in other.