It is possibly the world's best-known mobile, but it ended up at the bottom of the Geekbench 2 technical evaluation of the UK's most popular phones.
The test measures processor and memory performance across smartphone platforms - if a phone has a high score, it will work well when photo-editing, playing games and using apps.
The results revealed Samsung's Galaxy S4 was almost twice as fast as Apple's star phone with Samsung's Note 2 also scoring higher in the Geekbench pecking order.
Sony, Google, Blackberry and HTC smartphones also outranked the iPhone 5 for tasks such as games, pictures or apps.
The low score will be a disappointment for the US giant's huge fan base who tend to believe Apple's products are superior to all their competitors.
"Undoubtedly, Apple will upgrade its next iPhone with an improved processor when it launches later this autumn," Which? said.
"For the moment, Samsung’s Galaxy S4 is the phone to beat when it comes to speed."
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