Well, I would argue the GigaRumble should be renamed to the Top30Rumble. I was the one who created the meleeTop30rumble. The name make sense to me. Top30 is self speaking, unlike GigaMeleeRumble which confusingly seems to be opposite of nano/micro/mini, i.e. refers to the size. I presume it has some historical roots, but I joined robocode too late to know the meaning of the Giga name.
May be someone with longer presence can enlighten us about the Giga name history.