Geekbench found that older phones actually performed faster on older versions of Apple's operating system.
So, what's going on here?
Apple has released a statement to explain.
"Our goal is to deliver the best experience for customers, which includes overall performance and prolonging the life of their devices. Lithium-ion batteries become less capable of supplying peak current demands when in cold conditions, have a low battery charge or as they age over time, which can result in the device unexpectedly shutting down to protect its electronic components," the company said.
"Last year we released a feature for iPhone 6, iPhone 6s and iPhone SE to smooth out the instantaneous peaks only when needed to prevent the device from unexpectedly shutting down during these conditions. We've now extended that feature to iPhone 7 with iOS 11.2, and plan to add support for other products in the future."
The revelation of the intentional slowdown has revived discussion on Reddit and other corners of the internet that Apple deliberately throttles phones with each software update to encourage people to buy the latest model — known as "planned obsolescence".
John Poole, the founder of software company Primate Labs, wrote on Geekbench, that Apple had itself to blame for this theory taking hold.
"If the performance drop is due to the 'sudden shutdown' fix, users will experience reduced performance without notification," Mr Poole wrote.
"Users expect either full performance, or reduced performance with a notification that their phone is in low-power mode.
"This fix creates a third, unexpected state.
"While this state is created to mask a deficiency in battery power, users may believe that the slowdown is due to CPU (central processing unit) performance, instead of battery performance, which is triggering an Apple-introduced CPU slowdown.
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"This fix will also cause users to think, 'my phone is slow so I should replace it' not, 'my phone is slow so I should replace its battery'. This will likely feed into the 'planned obsolescence' narrative."
On Slate, technology writer Will Oremus said Apple's secrecy allowed conspiracy theories about planned obsolescence to thrive.
"More than anything, this episode simply underscores that iPhones really do degrade rather quickly over time for such an expensive product," he wrote.
"Planned or not, the result is still obsolescence. It shouldn't have taken so long, after so much obfuscation, for us to find out."
Despite the fact that iPhones are likely to work faster on the older software, Mr Poole urges customers not to avoid software updates.
"If you stuck with an older version of iOS, then what would happen would be your phone would be fast, but it might crash randomly," he told US business news network CNBC.
"So that's really not an ideal situation if you're relying on your phone day to day, like most of us are. The other problem with holding back on security updates is you lose the security improvements and fixes that Apple makes with every release, thus putting you in danger of … hackers and whatnot."
