The supersupmarine tech cost around 30 IPCs to achieve and a submarine (SS) cost 8 IPCs. So If we consider a fleet of 72 IPCs we see that BBs are never really a choice if one will invest 78 IPCs (6 subs + super sub tech). Break even seems to be around 72 IPCs for BB vs SS (considering super subs tech)! I know this more of theoretical than practical work, but I consider it interesting!
3 BB (24IPCs/BB)
Cost: 72 IPCs
Att: 34 = 12
Def: 34 = 12
Hits: 6
5 super SS (30 IPC tech + 8IPCs/SS)
Cost: 70 IPCs
Att: 53 = 15
Def: 53 = 15
Hits: 5
1st combat cycle
sSS scores: 15/6 = 2,5 hits -> 3 BB left (absorbed by 2-hit rule for BBs)
BB scores: 12/6 = 2 hits -> 3 sSS left
2nd combat cycle
sSS scores: 33/6 = 1,5 hits -> 2 BB left (opening fire means no return fire from casualties)
BB scores: 24/6 = 1,33 hits -> 1,67 sSS left
3rd combat cycle
sSS scores: 1,673/6 = 0,83 hits -> 1,17 BB left
BB scores: 1,174/6 = 0,78 hits -> 0,89 sSS left
4th combat cycle
sSS scores: 0,893/6 = 0,44 hits -> 0,72 BB left
BB scores: 0,724/6 = 0,48 hits -> 0,41 sSS left
5th combat cycle
sSS scores: 0,413/6 = 0,20 hits -> 0,52 BB left
BB scores: 0,524/6 = 0,35 hits -> 0,06 sSS left