The Radeon HD 4830 looked pretty good upon its release, but some cards that made it into the hands of reviewers and retailers are, in fact, not what they should be. AMD has just released a statement about the matter, which says:
AMD has identified that, in addition to reference samples of the ATI Radeon™ HD 4830 boards sent to media with a pre-production BIOS potentially impacting the card’s performance, a very limited number of ATI Radeon™ HD 4830 boards were released to market with the same pre-production BIOS. This is in no way hardware related, and an updated BIOS fully resolves the performance limitation.
Through consultations with AMD board partners, it has been determined with a high degree of certainty that fewer than 400 ATI Radeon™ HD 4830 boards from one AMD board partner, HIS, have reached the market with the pre-production BIOS incorrectly provided by AMD. As only a small number of HIS-branded ATI Radeon™ HD 4830 cards are impacted, we ask any customers that purchased an HIS-branded ATI Radeon™ HD 4830 to test the board using the GPU-Z utility (available at http://www.techpowerup.com/gpuz). If the GPU-Z utility reports fewer than 640 shaders, please visit the HIS website for information on how to update the card BIOS via a downloadable install utility.
If you've purchased one of these cards, you will very much want to check and be sure you aren't leaving some performance on the table.
As I noted in the comments to our Radeon HD 4830 review, our 4830 card was one of those affected. I've already confirmed a minor performance increase with an updated BIOS. I plan to update the numbers in our review, but doing so may take some time due to other pressing obligations.