No perceivable performance difference between iPad 4 and Air.
I did one better and did a DFU restore (w/ fresh install, no iCloud, no Siri, etc.). IOS 7 is still a stuttery mess for me - no improvement from the lag that plagued the 3/4 under iOS7. I'm doing a swap this afternoon to see if, in the highly unlikely case, it's a hardware fault.
I would reset to factor and clean out the old code. Mine does not have any of the issues that you face but I agree with you, I do not notice a difference beween 4 and 5 in performance.
I did one better and did a DFU restore (w/ fresh install, no iCloud, no Siri, etc.). IOS 7 is still a stuttery mess for me - no improvement from the lag that plagued the 3/4 under iOS7. I'm doing a swap this afternoon to see if, in the highly unlikely case, it's a hardware fault.