Eipper's old Northern called "Horse" is/was more than 80cm. Some of the relocators in the Nt reckon they have seen one metre long northerns. A bit like the Unicorn (a 60cm long Australian Bass) , im yet to see a picture of one of these beasties next to a measuring device.
Nt northerns no doubt grow to the largest lengths though.
As for easterns, some kicking around on the downs will be in the high 60's, but i can not believe in any being a metre long.
Cheers,
Dave.