I'm waiting for my iPad3, iPad4 and both iPhone5 units we have in the house until at least iOS8.x comes out...![]()
Had it running on my iPhone 5 20 minutes after it was released. Smooth as butter. And some of the new features are awesome. Especially love the new notification centre widgets. My favourite thing is actually being able to summon Siri (when plugged in) with "hey Siri". Fantastically useful in the car.
I'd update your iPhone 5 and iPad 4 (same CPU) with iOS 8 right away, no worries there. Just don't upgrade to iCloud Drive, or you'll lose access on the iOS 7 devices.
From this thread, since I had no issues with iOS 7, I'm getting the sense that upgrading might be okay. Or I might wait for 8.1, like I did previously, waiting for 7.1 (which was a very good move). Not sure...