With just over two weeks until the supposed September 10 iPhone 5S launch event, rumours of what to expect from the new iPhone are flowing in thick and fast.

The latest report comes from Fox News anchor Clayton Morris, who claims that his sources are telling him that the A7 chipset inside the upcoming iPhone 5S will offer a 31% speed boost over the current iPhone 5.

"I'm hearing it's very fast," said Morris in his tweet.

Given the A6 doubled performance of the previous A5 chipset when it was unveiled in the iPhone 5 last year, a 31% performance boost is not quite as big a step up, although rumours are suggesting that there could be a lot more to the iPhone 5S than just a power boost.

Motion tracking the next big thing?

Shortly after his chipset tweet, Morris was back at it, tweeting that he's also hearing about a dedicated motion tracking chipset in the upcoming Apple smartphone.

While details are obviously scarce, Morris himself argues that it "should be an interesting camera upgrade".

Of course, the rumour mill has always run overtime in the leadup to iPhone launches. Combined with the reported fingerprint scanner, 13MP camera with dual-LED flash and wireless charging, the iPhone 5S is looking like a much bigger jump up from the current iPhone than the iPhone 5 was from the iPhone 4S.

However, how many of the rumours actually come true will only be confirmed when we actually get to see the device. Fortunately, that is probably only a few weeks away now.

• Want a full run down of all the latest iPhone 5S rumours? Check out our ultimate iPhone 5S rumours page

Could Apple possibly be planning to add another colour to its iPhone 5S line up? A reportedly leaked SIM card tray has offered the slightest suggestion that a 'gunmetal' grey option may be in the works.

Following the leaks of a champagne gold casing, these new pictures leaked out of Japan, may just indicate that a fourth colour is on the way, but naturally this should be taken with a large mountain of salt.

The iPhone has only ever been available in black and, more recently, white so the roll-out of new colour options for the iPhone 5S would be noteworthy.

In fact, it may turn out to be a headline feature in what is expected to be more of an incremental update from Apple.

Gung-ho

The new gunmetal photos arise from ASCII JP, the same source as the initial champagne gold casing leaks, so they shouldn't be dismissed out of hand.

The iPhone 5S is likely to be launched at a yet-to-be-confirmed Apple event on September 10, where we could also get our first look at the cheaper, more colourful iPhone 5C.

Do you think Apple go gung-ho with a gunmetal iPhone 5S? Let us know your thoughts in the comments section below.

• Meanwhile, here's everything you need to know about the iPhone 5C