also manifacturing variation could not be so bad that rated 3200 mhz had to be lowered to 2666 mhz because of it. i understand that higher end 4750g like apus were not desinged for low end mobos like A300-STX, but it still seems a major hardware issue for me.The CPU cores and memory controller run on entirely separate voltage rails (vCore and vSOC respectively, with the DIMMs themselves having separate voltage regulation circuitry close to the slots), regulated independently, and controllable independently, so what you say here makes no sense. The cores needing less voltage to reach/sustain their clocks should have zero effect on the IMC's voltages.
Besides, the 3200 spec for Renoir is at 1.2V, the stadard JEDEC DDR4 voltage. 2666 or even 2133 doesn't use a lower voltage than this. Of course, many XMP/DOCP settings apply 1.35V or higher for high clocking memory, which is less of a guarantee, but any modern IMC should handle that just fine (1.35V over 1.2V is a 12.5% increase - if the Renoir IMC can't handle that, they have a very serious manufacturing or design issue on their hands).
thanks for asking JZ and sharing all the information here though, it's good to here that they are working on a solution!