It is possible for you to revert back to 4.3.5 as Apple have not closed the signing window for it yet, but you will have to be quick. Apple will close the window on version 4.3.5 in the very near future.
If you want to restore back to 4.3.5 you need to download a copy of 4.3.5 for your iPad from our thread here -
http://www.ipadforums.net/ipad-hacking/24939-official-apple-ios-firmware-download-links-ipad.html
Once that is on your desktop, you will need to put your iPad into DFU mode following our guide here -
http://www.ipadforums.net/ipad-hacking/27489-dfu-mode-dummies.html
Finally, once in DFU mode, open iTunes and shift-click (windows) or option-click (osx) the restore button in iTunes and this will allow you to select the file you just downloaded onto your desktop.
iTunes will then revert your iPad back to 4.3.5.
This process is perfectly safe - you cannot brick an iPad. It has nothing to do with jailbreaking. It simply reinstalls stock 4.3.5 onto your device.
PLEASE NOTE - This will only work for a short period of time. Apple will stop signing 4.3.5 very soon. When they do, there is no going back for you. Also, YOU WILL NOT BE ABLE TO RESTORE YOUR BACKUP FROM 5.0. You cannot restore a newer backup onto an older IOS. The choice is yours, but please take on board the message about the backup!
Hope that helps.