To my speculations, teh D Star'd be *********************'d up in a single hour by the Lucifer. Well, at least heavily damage it...remember the city-destroying blue beam?
Have you seen the Gargant? Think of it ramming the Executor to death...you'd hear Palpatine saying to Vader, "dive, dive, dive, hit your burners!!!"
And finally, we have Alpha one making himself invulnerable, and simply cheat his own ship to possess a Flux Cannon, launch it to the DS's core...blast.
Or, furthermore, Alpha one could just mod the .tbl files and create a lethal missile probably inflicting 2000,000 teratons of force