Comrades Back to Back Medal: How much can you improve on the up?

Derrick Pienaar was a Comrades Marathon novice in 2014 and has his eye on a Comrades back to back medal in 2015. Derrick managed to finish the Comrades down run in 11:40 this year. He did approximately 1400km’s leading up to this year’s Comrades Marathon and felt confident that he would finish the race. He says he’s super fired up to go for his Comrades back to back medal next year. Derrick’s question is as follows: What would be a realistic goal for improvement, as far as time goes, for his Comrades back to back medal on the Comrades up run?