This is because the GPU has shedloads of deactivated units which, if they were switched on, could make the chip go like the clappers. A die-shot of Hawaii graphics processing unit shows that the chip may feature as many as 3072 stream processors (48 CUs)
AMD sells the Radeon R9 290X which is configured to feature 2816 stream processors (SPs)/44 compute units (CUs), 176 texture mapping units (TMUs) and 64 raster operating units (ROPs) and the Radeon R9 290 sports 2560 SPs/40 CUs, 160 TMUs and 64 ROPs.
Overclocker 8Pack claimed that the Radeon R9 290X may not be the fastest Hawaii-based solution possible and that AMD could release something better.
Talking to the Overclockers.co.uk forums, 8pack said that the 290X was not full fat and something could be done about it.
A conservative estimate for what AMD might have on the table is a ten per cent improvement on the Hawaii-3072 gpu. But the boost may be higher or lower, depending on the clock-rates, wind speed and butterfly wings and jumping Chinese.