It appears that iOS 5 will give new wings to the older Apple iPhones like the iPhone 4 and iPhone 3GS, that's what can be concluded following the publication by Anandtech (opens in new tab) of a detailed table that compares the performance of the aforementioned phones on the iOS 5 GM and older iterations.
The benchmark used is Rightware Browsermark and shows that the iPhone 4S using iOS 5 is the king of the hill, narrowly surpassing the Samsung Galaxy Tab 8.9 with a score of 89567. The iPhone 4 with iOS 5 GM reaches 51701 which is significantly higher than its score of 36675 on iOS 4.3.
Even the the iPhone 3GS on iOS 5 GM surpasses the latter with a score of 37276. In comparison, the iPhone 3GS on the older iOS 4.2.1 reached only 26151.
So apart from bringing a slew of new features like iCloud or wireless sync, iOS 5 could also help significantly boost the performance of Apple's existing smartphones and encourage Apple users to stick to their existing handsets.
iOS 5 will be released over the next few hours worldwide and will come shortly after Apple has outed iTunes 10.5 which supports iOS 5 wireless syncing as well as automatic downloads and iTunes in the cloud.