The current record for largest Slammer multi kill is 6 Artemises, by QD I think.
I think I can beat that with 6 direct kills, one where my slammer did the most damage to it that when it was finished up I got another kill. Delenda Est, just before the 2nd Strike package shows up and you've got to take on a lot of fighters burning towards you. One warhead, not dual-fire either. ('course, my computer crashed later when the Imperieuse showed up, but you can't have everything). It's not much of a margin, and was the result of some rather nice circumstances and many replays of Delenda Est (For enjoyment, I seem to have beating the mission on Medium down a pat)
Maybe I should clarify that this was 6 direct, 1 partial for a total of 7.
And, Battuta, it might need some patching, it's tougher than Forced Entry by a large margin. (To be fair, I completed FE first go in a Zeus, I think it was). DE took a few attempts, but I enjoyed every minute of them, personally. But a lot of people are complaining, so it does suggest that there are problems with it.