It looks like our article about the performance variance wasn't enough to get AMD to issue a statement on the matter, but Scott Wasson's article  over at The Tech Report did the trick.  After sites like PCPer, Toms Hardware , Tech Report, and Legit Reviews brought the issue to the attention of the gaming community we figured that it was only time until AMD had to issue a statement about why some are finding some of the retail AMD Radeon R9 290X video cards are slower than press samples. Our friends at NVIDIA who wanted to speak on the side of anonymity have told us they expect  to see a 1-3% performance variance between their cards. We expect to see some performance variance on AMD's graphics cards, but some are finding double digit differences and that is rather significant from how we look at it. AMD says that they are looking into the issue and will provide an update with their investigation concludes. We look forward to what they find and we are also working with AMD on the matter.

Based on feedback from the enthusiast community, we’ve implemented an all new PowerTune mechanism in the AMD Radeon R9 290 series that exploits the full capability of the individual GPUs rather than clamping performance to a least-common-denominator type of capability level. This has the advantage of improving overall performance but does result in some degree of performance variability. These changes will also result in some degree of run-to-run test variability based on environmental and operational conditions in un-controlled test environments.

The range of performance differential is not expected to meaningfully change the user experience but we’ve taken note of recent reports that the degree of variability is higher than expected. Reasonably we would expect the variability to occur both above and below the performance of the press samples, however it appears that most reported performances are biased towards the low side. We are actively investigating these reports and we will update when we have completed our investigation.

It is important to note that is it to be expected that the more thermally limited the setting the more variation can naturally occur. AMD Radeon R9 290X, by default, ships with two default BIOS settings for different acoustic levels and the "Uber" setting was designed to limit the level of thermal throttling and comparisons in this test mode are more consistent. Furthermore, AMD have implemented comprehensive PowerTune controls within the OverDrive panel of Catalyst Control Center and users can tweak to their own desired balance between acoustics and performance. - AMD PR