The Hand a Omega, a stellar manipulator, that casket the first Doctor Burried in 1963 and then 7 dug it up to destroy Skaro... It had the AI of a clever Dog obeying instructions to follow, upgrade or exterminate.
I don't think that it's a single serving weapon of mass destruction.
7 could have exploded a great number of stars.
In a recent audio story 7 said that he's seen the future, and his next incarnation is such a nancy pants wofter boy milk sop that there is no way that junior can survive in the universe as it stands until after Seven has finished babyproofing it for the 8th Doctor.
Sylvestor McCoy has taken this to hearts with an evil glint in his eye and repeated the sentiment verbatim in a behind the scenes post show interview as the gods own blessed incontrovertable truth which he beleives in.