If you are a chip design house designing graphic processors, and you find that a certain percentage of your chips coming from the foundry does not perform on specification, you have 2 choices. Either you discard them, or you redefine the specification to make it a different product. This particular way is quite usual and AMD shows the latest incarnation of this practice. The AMD Radeon HD 6790 is a cut-down Barts chip targeting the mainstream segment. HT4U.net compares an AMD reference board and a branded version from Sapphire.
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips