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I like the glowing lightning cable!

No, the iPhone 6 is fine. The only two lags I've seen (and they are iOS related since they are identical each time). Swiping out tabs in Safari while horizontal leads to a brief pause and turning the iPhone horizontal in Messages causes the screen to go black for a moment.
 
The lag is only for the 6+.

The iPhone 6 renders at 2x but the 6+ renders at 3x and then downscales. Its more demanding...
 
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