WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
In a properly designed circuit very little to no difference, the Aikido is supposedly designed to have good power supply immunity. Hopefully they all sound the same, but if they don't you need to either figure out why and fix the problem or as some audiophiles do just accept it and choose what you think is the best sounding rectifier.
After 65 years of listening to, building, buying, and measuring amplifiers, I have yet to discover a difference when changing a rectifier. Almost like saying 'will my car run better if I charge the gasoline on VISA, or MasterCard?'
There were certain admittedly rare 5Y3 variants like the WGT which were usually indirectly heated, and did not entirely adhere to the original specifications of the 5Y3G either, based on my experience I suspect the Sovtek probably performs very similarly to the WGT type.
Your point wrt to the rectifier forward drop is valid though, and if using a vintage transformer designed for 110 - 117V power you can end up with voltages 20 - 30V higher than expected.
One could also make the argument that the 6L6GC is not a true 6L6 because it differs in some significant parameters like plate voltage rating and dissipation from the original.