90CU Navi(1.5x SP of Vega20) wouldn't be in 600mm2 range, +10CU don't take up extra 80mm2.I was actually comparing it to the 6800/6800XT.
My point is they still had to cut down the CUs to get that area. Vega 20 is at 330mm2 but grow to 520mm2 with Navi 21. 1.5x SP of Vega 20 will push it to the 600mm2 range.
Going from Vega 8 to Navi 12 will double the iGPU size as well.
Navi 21 has 128MB IC and 256bit GDDR6, which take a lot more space than HBM2, that's why Navi is so much bigger, of course not just because of them.
RDNA1 CU is ~2.1 mm2 and I don't expect RDNA2 CU to be more than 2.5 mm2 in the worst case.
It's hard to tell If Rembrandt IGP will be really 2x bigger than the one in Cezanne, I didn't even see anyone measuring just the IGP in Renoir or Cezanne to begin with.
BTW does It even matter If It's really 2x bigger? 12CU RDNA2 would be better than putting for example 16CU Vega, which would need to have lowered clocks to fit into the same TDP as 8CU Vega. RDNA2 is way more power efficient compared to Vega.