As wild rumours continue to swirl around the iPhone 6 release date this 2014, separating the credible stories from the downright speculative seems a difficult task.

When is a rumour but a rumour and when it is more believable? The gauge for many Apple watchers is the source, specifically its credibility. That is why Ming-chi Kuo of KGI Securities attracts attention because his previous calls were spot on.

And most of his forecasts were based on gathered intelligence from the Asian supply chain - in Taiwan and mainland China specifically, where Apple's iOS devices are manufactured.

Drawing projections from the supply chain, according to DigiTimes, is supported by solid information, most of the times at least.

For instance, "when Apple is getting a product ready for the market, the product is in the supply chain pipeline 6-9 months before Apple even announces its launch," said the Taiwan-based publication in a recent report.

That is like saying that a big bulk of iPhone 6 rumours emanating or provided by supply chain insiders enjoy some semblance of truth. And in the second half of 2013, the Apple supply chain discourse is dominated by three key specs and features that are briefly detailed below:

A8 chip in 64-bit mobile computing standard

Apple pulled a surprise when it pushed out the A7-powered iPhone 5S, which boasts of 64-bit mobile computing capabilities. But the same will not happen with the iPhone 6. As early as last year, the popular assumption is the next iPhone will carry another 64-bit processing chip, likely A8.

This guesswork is anchored on persistent and consistent supply chain chatters, the latest of which is the supposed takeover by TSMC of the full processing chip production that will be used with the iPhone 6 and the 2014 iPads. The news also suggests that Samsung is off the iOS device supply chain but will be back or the A9 CPU production on 2015.

The stories also alleged that TSMC is getting 100 per cent of the A8 chip manufacturing duties to ensure that production and release calendar of the iPhone 6 will happen as scheduled.

Sapphire glass cover

Sapphire was earlier introduced to the iPhone supply chain when the material was first employed as protective coating of the iPhone 5 rear camera lens. Then in the iPhone 5S, sapphire was again used as transparent and tough covering for the new Home button, underneath of which the Touch ID fingerprint scanner is embedded.

In the iPhone 6, reports claimed that sapphire will play a bigger role - as the glass cover of the bigger iPhone screen. Proof of this, according to Apple Insider, is the recent acquisition of Apple that corners a three-year supply of 4.5-inch sapphire display.

Now this supply chain development appears to confirm two things about the iPhones 6 - that its front panel is no longer guarded by Corning Gorilla Glass and its screen size is stretched to 4.5-inch, at the minimum, from the 5S' 4-inch profile.

Touch ID and mobile payment

Another supply chain rumour is that Touch ID will be enhanced for the iPhone 6 release. According to Business Insider, Apple CEO Tim Cook has strongly hinted that Touch ID fingerprint scanner will serve not only to keep the iPhone exclusive to its owner but also to shield user's data from being accessed by hackers.

Apple is ramping up the role it plays in the e-commerce sector and to that efficiently, the company is making full use of the robust security that Touch ID offers in mobile payment transactions.

"Because (Touch ID) makes your phone almost completely secure, the iPhone suddenly becomes an almost perfect mobile payments device," Business Insider said on its report, adding that this tool could prove as the next big thing from Apple.

And as if to confirm, Cook declared in Apple's earning call last January that "The mobile payments area in general is one that we've been intrigued with, and that was one of the thoughts behind Touch ID."

The iPhone 6 release date, likely with the above mentioned killer features, is predicted by analysts to happen between June and September 2014.