Really? Polaris hits 185W at 1340 MHz with 36 CUs (RX 580). Vega hits 210W at similar clocks (1410MHz boost, but that's not always sustainable) with 56 CUs. 25W for 20 CUs? Even subtracting the HBM advantage of ~40W (landing the 580 at ~145W, and the Vega 56 at ~205), that's noticeably less power per CU. Not accounting for VRM losses (which should be roughly linear, and thus safely ignored) and uncore (which is pretty much impossible to estimate), that's a difference of ~10% (3.66W/CU vs. 4.03W/CU). Not a massive difference, but definitely noticeable. Of course, the RX 580 is clocked around Polaris' upper limit, which skews the numbers, but every miner out there will tell you Vega scales very well for power when underclocked and undervolted, so the advantage should stick around when slowing down as well, even if it shrinks a bit.
Clock speed isn't the only determinant of power draw, and remember, manufacturers are free to define specs however they like. "TDP" and "base clock" doesn't necessarily mean the same thing in the embedded/digital signage world as in consumer gaming - which would make sense, as gaming PCs and digital signage boxes run very different workloads in very different environments. If "base clock" meant "the GPU will never clock below this limit EVER under load", GPUs wouldn't power throttle in FurMark. While the e9550 is no doubt heavily binned, I sincerely doubt it could sustain its base clock under a 100% 3D load such as any modern gaming load. Of course, I might be wrong. But demanding 3D is not what those cards are used or made for, and thus not specced for.
