Hi!
Here you have a very disappointed 6 plus, first day buyer. So far the 6 plus have been laggy in general animations (the infamous rotation, zooming in and out of apps and even scrolling between homescreens), spotlight, third-party keyboards, loading App store and most importantly: SAFARI!! To have the slightest chance on performance close to Safari on ios 7 on the 5S I need to close my three tabs and disable JavaScript. Icloud integration is not on and I regularly clean history. And the tabs constantly reload and I very often get a notification in safari that it could not render the page. Is any of the mentioned better on 8.3?
How about memory management? While having following apps in the background: safari with 3 tabs, music app and pulse, monitor activity shows that the available amount of ram only is about 5 percent!!! And that on ios 8.2!
It has slowly become better, but in all honesty this it's not what I expected from a top notch IPhone....