I did some pack-size estimates based on the 123 KWh CT pack and some composite factorization for number of cells used. TL;dr is I think the LR Model Y will have a 82 KWh pack and the Gen 3 car will have a 41 KWh pack, all of which are capable of charging on 800v DCFCs like Supercharger v4.
Cheers!
Any DCFC capable car, even a 400v one, is capable of charging on a v4 charger... 800v (actually closer 1000v) is just the max the charger can supply. And Tesla's one 800v architecture vehicle (the CT) can reconfigure it's pack to charge on a 400V Supercharger/DCFC.
Are you saying you believe the Gen3 will also be an 800v pack architecture car?