"The 8750 Black Edition, perhaps with a Western Digital Caviar Black naming influence"
Pretty sure AMD's 'Black Edition' products have been around longer than Western Digital's Caviar Black.
And a Black Edition AMD chip merely has an 'unlocked multiplier', as it is called, which allows the speed to be set manually by those who know how, and if the chip can handle it. And if it can't, AMD isn't liable to replace the chip because doing so is what those in the industry call 'Overclocking' and all companies have a policy where 'Overclocking' voids the warranty, because this kind of activity pushes chips beyond their intended use.
I suspect this is what the bit about a 'Clock Multiplier Control' refers to. It may also refer to elements of the revised AMD Overdrive program, which is still 'Overclocking' and is offered 'as-is', as these companies say. It is not uncommon to offer Overclocking software with major, high-end computer components, especially graphics cards, but even if there is official software, it is not considered a 'supported' function of the card or software- again, 'as-is'. It's supplied, but the user utilizes the software tools at their own risk. As well, it's not so much because of the 790GX, it's because of a secondary chipset called the SB750 that is also being fitted onto motherboards with 790FX chipsets for the highest-end hardware (GX is technically a step down from the FX).