Tom has a damn good source at PS when it comes to hardware
If so and taking what he says seriously...
The Xbox Series X has 56 CU's, so that means nothing without a clock speed to slap on. I doubt they can make a GPU as big as a Xbox Series X and maintain the clocks they're pulling on the PS5 without making cooling more extravagant and adding a fan. bigger chips are "wider", wider means less MHz possible because heat will increase a lot. This is a crux even Apple is facing with their M2 Ultra chips and lowest node available to men.
This is also different than the approach they took with the PS4 pro, where they doubled the chip from 18 to 36 CU's, PS5 is 36 CU's, for coherency sake and because they liked to turn half the CU's off on PS4 Pro to ensure perfect retrocompatibility with PS4 (and I don't think PS5 being 36 CU's as well is a coincidence), I'd wager 72 CU's should be more likely.
18000 MT/s a useless metric without the ram bit-width interface and/or number of chips. But considering 256 bit bandwidth, it's not a massive increase. 448 GB/s to 576 GB/s. I can see them going for 384 bit (12 chips instead of 8) and 18 GB of RAM, in order to hit 864 GB/s. I don't believe they could go for 24 GB of installed RAM and 16 GB is not possible with this configuration.