Alright just got it installed on my iPad 2. Testing out my little platformer game :
* Before the upgrade, i was getting roughly 15-17fps. Still impressively playable considering its an HTML5 action based game running on a mobile device.
* After IOS 5 upgrade, i'm getting 40-44fps! This is now very playable and almost like playing on a browser off your PC or Macbook :)!
I still have yet to try this on my iPhone 4. I was getting roughly 5-7fps off of it, yet strangely playable. Gonna post more results soon.