It doesnt seem to be GCN 1.1
http://www.hardocp.com/article/2015/06/18/msi_r9_390x_gaming_8g_video_card_review/3#.VYMmMlVVhBf
Hardocp reporting the large tessellation performance of the GCN 1.2. I suspect Drivers are the cause of its middling performance so far. Not enough to swap from a 290x but it seems like more of a refresh than a straight rebrand to me.
http://www.guru3d.com/articles-pages/msi-radeon-r9-390x-gaming-8g-oc-review,1.html
'When the AMD Radeon R9 290X was released, it finally had architectural improvements over the 7970 that increased the GCN version a bit. However, that was back in 2013 that the AMD Radeon R9 290X codenamed (Hawaii) was released. So here we are two years later, and basically we are getting a re-brand of Hawaii with the R9 390 and 390X. This time, no architectural improvements.
What does that mean as far as performance and specs go? Well if you look above at the specifications for the AMD Radeon R9 390X above (the one we are reviewing today) you will note it shares all the same specifications with the AMD Radeon R9 290X. Both the AMD Radeon R9 290X and AMD Radeon R9 390X are built at 28nm, have 2816 Streaming Processors, 176 texture units, 64 ROPs and 44 Compute Units. Both utilize 512-bit memory busses with GDDR5.
There are only three things that separates the R9 390X from the R9 290X. The first thing is a higher default stock GPU clock speed of 1050MHz versus 1000MHz on the R9 290X. The second is that the memory is clocked a lot higher this time around at 6GHz versus 5GHz on the AMD Radeon R9 290X. This brings the memory bandwidth up to 384GB/sec versus 320GB/sec. Finally, the R9 390X will come standard with 8GB of VRAM versus 4GB on the R9 290X.'
So 4GB Vram and an overclock..........