The results after installing the Arctic Accelero Xtreme IV with Kryonaut on my overclocked Sapphire R9 280 Dual-X. CPU running Prime95 small FFT, GPU running Kombustor. All fans running at 100%.
Before:
Max temperature of 92°C on the GPU. The GPU was easily the loudest part of the system, and quite annoying.
After
Max temperature of 58°C on the GPU.
So a significant temperature decrease after installing it. With the case fans running at about 400-500RPM and the stock fan curve on the GPU:
Max temperature of 71°C on the GPU. The HDD is now the loudest part of the system. I can live with that.