As far as iPhone 6 rumors go, few are more prevalent than the ones speculating Apple (AAPL 0.51%) will introduce two different sized devices to market later this year.

To be sure, we're already aware Apple knows the iPhone 6 needs a bigger screen. What's more, the latest supply chain rumblings support that assertion, saying one version will feature Apple's usual 4.7-inch display, while the other iPhone 6 could incorporate a massive 5.5-inch screen and be marketed as a "Phablet" of sorts.

According to the Fool's Steve Symington in the following video, however, Apple is walking a fine line between success and frustration by narrowing the gap between its phones and smaller tablet offerings like the iPad Mini. As a result -- and though Steve notes Apple has almost certainly certainly weighed the benefits of doing so -- shareholders need to remain cognizant of the risk a larger iPhone 6 brings in potentially cannibalizing iPad Mini sales. To hear Steve's full take on what this means for investors, please watch the video.