But as the video below illustrates with an eight-way speed test between all of the publicly released iPhone models since 2007, the truth is a little more nuanced.
Earlier-generation models, led by the iPhone 3GS and followed by the 3G, 3, and original iPhone turned out to be the quickest to shut down. As EverythingApplePro observes in the video, it seems that something in iOS 7 leads devices running it to take longer to shut down.
Another surprise comes when all eight models race to boot up. Predictably, the meatier hardware in the four newest models allows them to reach a home screen first, but interestingly, the original iPhone is quicker to boot than the iPhone 4, 3GS, and 3G. All the models shown have the latest updates, so it makes sense that the iPhone 4 might struggle to run iOS 7 quickly. Apparently differences in the earlier version of iOS run on the original iPhone make up for its hardware deficiencies when compared with its successors.
The conclusion reached in the video is that it's not worth upgrading to the iPhone 5S for its marginal speed improvement over the 5 alone. But to me it seems the real issue revealed (or reinforced) here is that you might want to think twice before upgrading to iOS 7 on your iPhone 4.
Did anything in this test surprise you? Let us know in the comments.