It doesn't matter what iOS was on your iPad when new, it can't be downgraded. If you want to jailbreak it, you'll have to wait for the next jailbreak release.
BTW, when did you downgrade your iPhone 4S? At the current time, it's not possible to downgrade an iPhone 4S.
The iPhone 4S was jail broke before upgrade to 6, was able to restore this was around December
If you google it there are many YouTube videos. Want to say it was by shinysr???? On YouTube.
According to it, it's not possible for you to have downgraded your iOS from iOS 6 to iOS 5.1.1 after the signing window for iOS 5.1.1 closed last September 21st.