It depends on which card you're looking at. With MSI, they seemed to have gone full rebrand and overclocked the components they already had on hand, like the memory, which increases power draw dramatically (R9 390X Gaming as an example). But, I've seen results from other R9 390 cards that have better and quieter coolers than the R9 290, along with the same power draw (within 10W difference in one case, Sapphire Nitro), and almost all R9 390 samples I've seen have been just as fast as the R9 290X.
So like I said before, these aren't straight rebrands. There are definitely changes in the chip and performance is up, but AMD's obviously using what existing hardware they have to fill in the gaps.
At least its only one generational rebrand with Hawaii, Bonaire and Tonga. Pitcairn has been re-used three times to arrive at the R7 370, which is the same record as the G80 architecture. Fermi at the low end has been rebranded by Nvidia four times.