Earlier quoted context omitted.
Usually, apple tries to improve firmware speed after they add features. I found that staying updated is the best policy.
Unless you're trying to run iOS 7 on the iPhone 4 or iOS 6 (or was it 5?) on the 3G. There are definitely times where it DOES NOT END WELL even though the device technically supports the upgrade. A better policy is to wait for reports and then upgrade after a few weeks if they're positive.
A better policy is to wait for the official releases rather than buying a UDID slot from a dodgy website.