Changing up the reference cooler on an R9 280X is bound to have an effect on both the noise produced as well as the temperature of the GPU and hence the frequency that the GPU runs at.  The reported 'base clock' of the GPU is 1100MHz with a top speed of 1150MHz and an effective memory speed of 6.4GHz with controllable voltage to ensure that enough juice is getting to the GPU.  [H]ard|OCP saw a significant decrease in the temperature of the GPU and when they overclocked the card they did see an increase in performance, you can see exactly how much in the full review.

"The SAPPHIRE TOXIC R9 280X is here and is screaming to be overclocked. This bad boy is suited with the new SAPPHIRE Tri-X cooling system, a hefty factory overclock, and is built to push overclocking to the next level. It will have some fierce competition going head to head with the ASUS GeForce GTX 770 DirectCU II and its overclocking ability."

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Graphics Cards