i like the idea of synergy vs diversity. Simplicity works well, if i were to ten box i'd have to have some mix of ranged and melee. ie:
pally tank
dk or druid tank
1 mage
2 elemental shammy
1 enhance shammy
2 ret pally
2 holy priest

this would be the makeup i'd go for strictly for the easy self preservation and dmg output available. Tanks would be a lil tricky, part of me would rather say go with dk and druid to maximize and diversify.

i'd also change it up and go with a simplistic group makeup of pally tank druid tank 4 ret pallys and 4 elem shammys (swapping one of each 4 group to resto if needed)