From the first post on 30th August about SS:
http://services.runescape.com/m=news/super-september-is-coming
Two Super Challenges have their own hiscore tables for a week each. Complete Farmyard Rampage and Bulldog as many times as you like to make it into their hiscores. At the end of the week, the top 1000 players will earn themselves 2 new titles as well as the gold version of the superhero outfit!
Seems to me like there won't be further rewards, although you can choose to get rank <1k in both events, I guess.