Just thinking about it - all of the suggested specs you'll get for a 4 man wil be one of the three following combinations:
- MT + MH + Util + CC
- MT + MH + Util + DPS
- MT + MH + DPS + CC

So we may be able to work out the combos based on the assumption you'll go a crusader and have wards for heals
- SK + Def + Dirge + Coer
- SK + Def + Dirge/Troub + Brig/Lock
- SK + Def + Brig/Lock + Coer

- Pally + Mystic + Troub + Illi
- Pally + Mystic + Dirge/Troub + Swash/Lock
- Pally + Mystic + Swash/Lock + Illi

All combos have their merits - with only the real difference between the groups being where they sit for DPS and survivability curve

DPS <-------------------------------------->Survivability

I would suggest any group with an SK tank leans more towards the DPS end (at the cost of suvivability) whereas Pally teams tend to be more towards the suvivability end with less DPS