GDDR6X or GDDR6 memory?
if the rumours are to be believed would be 6X, would not make sense to go slower on the flagship gaming card vs the 3080. However it looks to use the slightly lower clocked 3080s memory speed and smaller bus of the 3080 resulting the same bandwidth as the 3080 rather then 3090. All else equal that will be why you will see a very tiny performance deficit to the 3090, order of 1%-2% I expect in benchmarks and likely less in games.