We do not have any document where this is being evaluated as the processor is just tested and certified to work as expected when using default settings. In such case, we suggest on using the system defaults to prevent any problems caused to the processor.
Even though the IGPU does not interfere with the processor's cores, one thing you might consider is that if the IGPU will be used, that will represent more heat to the whole die, which may decrease the heat/power headroom that could be used to clock up the processor while being overclocked.
