While both versions will likely be announced at Apple's big event, there have been many reports in the past few months that say Apple has run into production issues that could delay the release of the 5.5-inch iPhone 6.
Famous Apple blogger John Gruber has posted about the potential issue, discussing both the draw of the larger screen and battery of the 5.5-inch iPhone 6, as well as its probable scarcity.
We can square this circle pretty easily. My guess is that both phones will go on sale, officially, at the same time, but that the 5.5-inch model will be in short supply initially - perhaps severely short supply. In short, the 5.5-inch iPhone might be this year's gold iPhone 5S - very hard to get for the first few months.
Gruber also predicts that many will opt for the larger, 5.5-inch iPhone 6, due to its potentially massive battery and stunning display, which he says will boast a stunning 2,208x1,242-pixel display, meaning an incredible 461 pixels per inch.
The bigger battery also explains, partially, why I project that the 5.5-inch, and only the 5.5-inch, iPhone will get a super-high resolution screen (461 PPI, I'm guessing, give or take a pixel or two per inch) and will run at @3x retina resolution. More pixels consume more power.
The 5.5-inch iPhone has room for a battery that is way bigger than the one in the 4.7. According to purported supply chain leaks, about 50 percent bigger. So it can provide energy for the power-hungry 461 PPI display and still have plenty left over to give the large iPhone unprecedented (at least for iPhones) battery life in real-world usage.
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