Polaris 10 to a 390x, 390x has 2816 ALU's, Polaris 10 rumors put it at 2560 ALU's.
Also transistor counts for a 390x is 6.2 million, It looks like Polaris will have around ~8.6 million that puts it at Fiji level transistor counts (granted you have to reduce that amount when comparing to Fiji due to the HBM memory controller size).
Means they put much more transistors in the front end changes.
Going by this, they need a similar clock level as Pascal to get to the 1070/1080 performance level. IF they are stuck at what they are now, you are going to get r390ish levels maybe a bit more.