if you do not need any apps that require ios7 to install then stick to ios6 for ipad 2. Sure, you can turn off some features to make it faster for ipad2. However, the memory footprint of ios7 is a lot more than ios6.

On fresh boot up, my iphone5 ios6 have free memory of about 600mb. With ios7, it's 400mb. And I already turn off things like parallax effects and some other features that slow down the phone.