News ASRock Registers 16GB RX 7800 XT Graphics Cards

The first SKU is probably a mid-range model, while the PGW could potentially be the flagship SKU with beefier cooling and/or a higher factory overclock.

NOPE, both the cards are exactly the same. The other one is just a WHITE variant of the previous SKU, hence the suffix PGW. "W" for White edition.
 
By the way, it appears that both cards would also feature a custom triple-fan cooling solution in a 2.5-slot form factor, and will come in factory-overclocked flavors.