2 power connectors? So, the 400+ TBP claims are not true for the reference cards? Doesn't give me much hope for it competing with the 4090 even in rasterization then.
I don't think AMD will get anywhere close to that level of efficiency, but to be fair, benchmarks of 4090 with 300W power limit gets about 91% of the performance relative to "full" performance at 450W. If AMD has 10% efficiency advantage, they'd be able to match 4090 full-power with 300W.
However, AMD is slightly behind nvidia in terms of fab process this gen, and MCM will have at least a small performance penalty compared to monolithic, I simply don't see the winning on pure efficiency this gen.