To celebrate the 21st Grand Challenge, the Rusty's have added an optional extension to the 2007 ride. As long as you have completed a past run you can choose to do this extension and get a second badge if successful. To get the second badge you must complete a further 500k's while still staying within the 1st 24 hour period.
A really big ask! It means that you would have to do the first 1600k's in about 18 hours or you wouldn't have a chance of finishing the next 500. As I usually do the run in a comfortable 20-21 hours I'm not sure if it's worth giving it a go - there'll be no time for any mucking around!