I'm usually the only person wobbling about in a Kate attacking a base, so until I practice offline I can't vouch for the efficacy of the 800kg SAP round, except to say that in a hot zone, a couple of flights are usually all that's necessary to drop a SB, however you need to hit the target to get maximum effect. I know that sounds oxymoronic, but a dead-on hit generates more damage points than one would expect, where a very close splash delivers less than expected.
I suspect I only need a couple of flights due to other people damaging the SB before, during and after my flights.