Have a look at the releasenote for every 11.x.x release note and judge for yourself.
Also have a look on
https://www.cvedetails.com/product/15556/Apple-Iphone-Os.html?vendor_id=49
CVEdetails gives you an idea of what security vulnerabilities that has been found.
Spend a day reading up on it and if you still feel that a slightly slower phone is your main concern you should think again.
Also have a look on
https://www.cvedetails.com/product/15556/Apple-Iphone-Os.html?vendor_id=49
CVEdetails gives you an idea of what security vulnerabilities that has been found.
Spend a day reading up on it and if you still feel that a slightly slower phone is your main concern you should think again.