from about six month my "HIS R9 270X IceQ X² Turbo Boost Clock 2GB GDDR5" runs at 1000MHz (this is what "Radeon settings" shows in "overdrive global" page).
Stock clock should be 1140MHz. Even if I change the clock, the card always runs at 1000MHz (450MHz in idle mode).
Radeon software is the latest version available, 17.4.4. Tried to downgrade to the version 16.7.2 and 16.8.2, which I'm sure they worked when I used them last year, but now it runs at 1000MHz. Obiouvsly I tried even a clean driver install.