Inteluser is discussing performance per TLFOP. All of these are wishy washy based on speculation and rumours, but if that leaked 2304SP 480 is running at 1266Hz and is barely faster than the 2816SP 1050MHz 390X, then AMD has not improved at all there. Complete stagnation.
TFLOPS are definitely not best indication of potential performance - in that case 8.6 TFLOPS Fury X should easily kill Titan X/980 Ti (6.2/5.6 TFLOPS) and compete as almost equal with GTX 1080 (9 TFLOPS).
Btw, what if base clock of RX 480 is circa 1100 MHz and could be OC to 1.4-1.5 GHz?