To be probably named as the Radeon R9 480 and R9 480X, the two Polaris 10-based graphics card should be a part of the mid-range lineup but the results look quite promising as these offer somewhat higher performance compared to the Radeon R9 390 and R9 390X.
According to the results provided by Videocardz.com, the faster Polaris 10 graphics card should be close to the Radeon R9 Fury graphics card, at least in 3DMark. This also means that it should be faster than the GTX 980. The slower Polaris 10 graphics card, which should probably end up as the Radeon R9 480, could end up a tad slower than the Radeon R9 390X, but faster than the GTX 970. Videocardz.com also provided Crossfire results where two Radeon R9 480X are faster than the GTX Titan X graphics card, socring 25830 in 3DMark.
According to Videocardz, both Polaris 10 graphics report the same 8GB of VRAM and same 1266MHz GPU and 1925 and 2000MHz memory clocks. Bear in mind that these are just 3DMark results that could be using both older drivers as well as lower clocks but at least gives us a general idea on the performance.
Of course, we should know soon as AMD has already announced its Computex 2016 event for June 1st.