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The interesting thing about displays is the human factor. We truly see what we want to see. Our eyes can find flaws in anything if we look long enough, we also confuse things like color temperature, contrast, and brightness. Low light contrast vision is almost off the charts to keep us be being eaten by lions at dawn or dusk.

Here is a funny story. We would take line workers and put them in dark rooms to look for image flaws. In the first hour or so, they would find too many problems. After 8 hours they would find no problems. The longer we gave them to look the more they would find.

It was quite a balance of making them wait when they entered the room before they could fail imagers...how much time per imager we gave them....and how soon we would need to pull them out.

You can see the same thing here every time apple puts out a new iMac.
 
Looking at them both in the Apple Store, the only difference I could see in sharpness on the 6+ display was if I held it absurdly close to my face (like 6-8 inches). At the normal distance I hold my phone, they both looked pretty much the same, other than maybe absurdly small typeface (e.g. a desktop website zoomed out completely).
 
I was referring to your contention that the 6 has a better contrast ratio than the 6+

Last thing I'm looking up for you...Apple's own website

Retina HD display
4.7-inch (diagonal) LED-backlit widescreen Multi-Touch display with IPS technology
1334-by-750-pixel resolution at 326 ppi
1400:1 contrast ratio (typical)
500 cd/m2 max brightness (typical)
Full sRGB standard
Dual-domain pixels for wider viewing angles
Fingerprint-resistant oleophobic coating on front
Support for display of multiple languages and characters simultaneously
Display Zoom
Reachability

iPhone 6 Plus
Retina HD display
5.5-inch (diagonal) LED-backlit widescreen Multi-Touch display with IPS technology
1920-by-1080-pixel resolution at 401 ppi
1300:1 contrast ratio (typical)
500 cd/m2 max brightness (typical)
Full sRGB standard
Dual-domain pixels for wider viewing angles
Fingerprint-resistant oleophobic coating on front
Support for display of multiple languages and characters simultaneously
Display Zoom
Reachability
 
Last thing I'm looking up for you...Apple's own website

Retina HD display
4.7-inch (diagonal) LED-backlit widescreen Multi-Touch display with IPS technology
1334-by-750-pixel resolution at 326 ppi
1400:1 contrast ratio (typical)
500 cd/m2 max brightness (typical)
Full sRGB standard
Dual-domain pixels for wider viewing angles
Fingerprint-resistant oleophobic coating on front
Support for display of multiple languages and characters simultaneously
Display Zoom
Reachability

iPhone 6 Plus
Retina HD display
5.5-inch (diagonal) LED-backlit widescreen Multi-Touch display with IPS technology
1920-by-1080-pixel resolution at 401 ppi
1300:1 contrast ratio (typical)
500 cd/m2 max brightness (typical)
Full sRGB standard
Dual-domain pixels for wider viewing angles
Fingerprint-resistant oleophobic coating on front
Support for display of multiple languages and characters simultaneously
Display Zoom
Reachability
But how do you know the 6+ is bigger than the 6 ;)
 
Enormous difference between my iPad 2 and iPhone 6 plus.

Between iPhone 5 and 6 plus? Not really as far as pixels are concerned. They're right when they say the human eye can't really tell past 300. I can't pick out pixels on the 5.
 
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