I'm not sure if there is a reliable method of killing superbattleships.
Best bet is probably Battleships. They have enough fire power to kill them in 1 turn, but they can only have 6/20 misses. Since accuracy is only 30% (I'm sure that's what I read somewhere), you have to get very lucky to take out a SBS with a Battleship.
It may actually be easier when they are in a larger fleet.
Definitely. Mixing SBS with anything weakens their effectiveness. It's just a toss up between killing something quickly (larger fleet with SBS mixed in), or slowly but with less losses (small, SBS only fleet).
