Microsoft has already noted that Windows PC users will see a performance drop due to the initial Spectre and Meltdown patches and it seems like Apple is not immune either. New benchmarks results circulating the web claim a 41 percent performance drop on an old iPhone 6. The single-core scores on the Geekbench test for the Apple A8 powered device reportedly dropped from 1,561 points to 924 points. Multi-core scores went down by 39 percent dripping down from 2,665 to 1,616 points. According to the blogpost on Melv1n, with the new patch, the least affected area is the memory, which saw a performance drop of 14 and 8 percent for single and multicore, respectively. The blog also states that the performance drop "could be influenced by the battery throttling" as well.
It should also be noted that the tests were done on non-consecutive versions of iOS. So, the tests were conducted on the iPhone 6 with iOS version 11.1.2 vs 11.2.2 instead of 11.2.1 vs 11.2.2. The Melv1n blog has since retracted the benchmarks citing personal threats to the writer’s address. He said, “I mostly share my knowledge on this site about my experience in technical product management. I updated to 11.2.2 solely for security purposes which I found mandatory patching the Spectre vulnerability. I shared my iPhone benchmarks just out of my own amazement about the numbers. That was it, those were just my benchmarks. Apparently, some took it as an absolute truth for others (which I clearly stated it was my own device only) and presented it that way on other sites without any nuance”.
In the aftermath of all this, Howtogeek also ran some tests of their own on the iPhone 6s, 7, 8 and 8 Plus and found out that the performance drop is not that huge. The iPhone 6s showed a performance drop of 10.4 percent in single-core and 17.5 percent performance reduction in multi-core. The iPhone 7 recorded a performance drop of 4 percent and 2 percent in single and multi-core tests respectively. The performance of the iPhone 8 and 8 Plus saw a negligible drop in both single core and multi-core tests.
All these results seem highly varied and it is more than likely that older iPhone users will find their phone slowing down further due to the new update. Still, to be on the safer side, we would suggest you update your phone to the latest version of iOS and get the battery replaced if you are still on an older generation iPhone.