VideoCardz says the launch date of the 20GB card is strictly dependent on the launch of AMD's Big Navi lineup:
This roadmap is yet another confirmation that GeForce RTX 3080 20GB will launch at some point, but neither Gigabyte nor Galax have confirmed the timing. According to our sources, the date is strictly related to the launch of the Radeon RX 6000 series, so it is definitely coming, it just happens to be dependent on a competitor.The GALAX roadmap puts the RTX 3060 at about the performance level of the RTX 2080.
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— HXL (@9550pro) September 23, 2020