@FeliApple: but the whole purpose of iOS 12 is to improve performance on older devices. Have you seen iOS 12 on the 6 year old iPhone 5s and original iPad Air?
I agree with others that you are missing out but I also get why you’re hesitant to upgrade.
Anything with 2 GB of RAM will run like new on iOS 12. My iPhone SE definitely feels like it’s new again.
iOS 12's performance is probably fine, maybe slightly worse (It is a very positive exception in that regard). Battery life is probably really low, if compared to iOS 9.
I have never seen a 5s on iOS 12. The only 5s I have used is now used by a family member and is running the original iOS 8 (bought late, it came from iOS 8 from factory). This is absolutely an anecdotal experience, but a family member has a 5s on iOS 12 and said that its battery was busted, worked poorly (at least on iOS 11) and it was too old. I told him that that was most likely false. The sole culprit of his phone working like that is the iOS update. I haven't tried it. Maybe iOS 12 improved it, I don't know. (I doubt it improved the battery life).
What I have seen and tried, is a 6+. Now, yes, I know: this is due to the anemic 1GB of RAM. This is probably a fringe case, just like the iPad 3 was (A5X didn't have enough power for a Retina display).
Battery life was two things: decent, if you take into account the amount of hours that it was getting with no context at all (which were around 7), and absolutely terrible, if you take into account what an actual non-updated plus should have gotten: I used a 7+ for a year (phone which I'd still be using, if it weren't for the fact that it's camera is broken, and after Apple outright refused to fix it, I was tired of it, and went back to my 6s), and I was getting 10-12 hours of usage. Also, performance was awful. Took ages to load and crashed all the time.
Same with the iPhone 7:A friend has one on iOS 12. Performance? Amazing. Faster than my 6s on iOS 9 in all regards. Battery life: Exactly the same on iOS 10... Half of what I'm getting on iOS 12.
It seems that Apple can't get everything right. When it manages to improve performance, it destroys battery life. Otherwise, it destroys everything.
I know what you are saying with performance. My iPhone 4 and iPad 3 were ruined by the last supported software updates as well. On iOS 12, I was reluctant to upgrade my older 5s and older iPhone 6, but glad I did.
Overall both devices are far more useful, and actually are quicker in some functions than before. I would suggest looking into reviews for your device in iOS 12, and confirm for yourself before making the change.
I don't want this to seem that I'm trolling or being negative on purpose, but I have always had the same gripe with reviews: Do people know how should their devices be working? I think people forget about how fast their devices were on the original iOS versions. (This probably applies only to battery life on iOS 12, as I said, performance is probably fine)
I will illustrate: I have seen people here say the iPhone 5c on iOS 10 is absolutely flawless.
I have it on iOS 9. It is great, actually, compared to what I should expect of a 32-bit device updated two versions of iOS. But it has absolutely no comparison to iOS 7. The keyboard has mild lag; is it absolutely unusable? No, actually, far from it, but it is there. Apps crash? No, but they take 3-4 times longer to load than what my iPod Touch 5G on iOS 6 takes. (One little fun fact: the iPod Touch is slightly faster on app launch than my 6s - yes, negligibly so, but faster indeed. That's how good iOS 6 was).
Back to the 5c: battery life. Atrocious. It should be around the same than the 5s. Furthermore, I have read that it should even have a slight edge over the 5s I was using, and the 5s had no Low Power Mode (It's on iOS 8, LPM was added on iOS 9). Well... It is horrible. 5-6 hours with Wi-Fi and light use with LPM since 100%, and 3 hours with LTE and outdoor brightness, again, LPM all along. I should be getting double with LTE, and 3 more hours with Wi-Fi. Everyone here says the 5c on iOS 10 is fine, battery life is decent, and that iOS 10 is a great surprise because of performance (arstechnica wrote a review saying that. I bet they didn't try one on iOS 7).
After writing the previous line, I looked up the review and skimmed through: it compares it to... iOS 9. And it even has worse app launch results than iOS 9: not a single one under a second. My iPod Touch 5G and 6s launch apps in under 0.8. My 5c is almost double that, and in some cases, more; yet I have read people saying iOS 10 was flawless and I should update without a sliver of a doubt, even if I were on iOS 7.
