Apple's decision to turn the battery swap for $29 is a smart one in that there will be more to gain than lost. Because along with upgrading your battery for a small $29 price, you still will suffer performance issues with new iOS that is more CPU intensive, designed to work on the faster chips with more cores. Most people will want the new features and the best way to get that is with new hardware. So, in addition to breathing new volts into your circuits with a $29 battery, you should stop doing the iOS upgrades as well to avoid slow running iphone.
Remember when we had those 486 CPU's in our computers? Do you think you could run windows 10 on them? Today, if you aren't using a minimum of 4 core processor, Google Chrome wouldn't perform very well.
The iPhone 7 had a 40% faster CPU and 50% faster GPU than the iPhone 6S. This is a big multi-generational jump and means the iPhone 8 is not only the fastest smartphone (excluding the X) on the market, but it is likely to remain faster than Android rivals well into 2019 as well. The 6 has a dual core processor, the 8 has a 6 core processor.
If you are annoyed by lack of performance as you become more dependent on your iphone for more things in life, budget for the 6 core iphone and be good to go for another year or two. If you want augmented reality features, then jump to the iphoneX.
BTW- I just received a note from TD Ameritrade that their stock trading app will now support the iphone X and it's Augmented Reality capability.
I haven't looked into what that means, ie reviewed the video yet, but it sounds interesting. Augmented reality for stock trading? Could that be like learning Option trading using real world market data for virtual classroom training?