Overclockers Club published a review on the Sapphire R9 280X Toxic
A quote from the article:
So there you have it, another custom built card from Sapphire that takes what AMD has to offer and bring it kicking and screaming to reach another performance plateau. Considering that the R9 280X Toxic is built upon the aging Tahiti XT core, the performance squeezed from this card allows it to play well above its price point of $349. Not to draw the wrong conclusion, but this card does what last year's HD 7970 6GB Toxic Edition card did and does just about everything better when you look at gaming performance and to some degree power consumption. Let's start with the gaming performance of the Sapphire R9 280X Toxic. Throughout the resolutions tested, the card was markedly better than the HD 7970 in every single test while delivering performance on par with or better than the GTX 770, again through each test. Depending on the test the R9 280X Toxic could deliver FPS results within a couple FPS of the GTX 780, which costs better than $300 more in most casesSapphire R9 280X Toxic Review @ OCC