The Furmark rendering on RadeonSI Gallium3D wasn't correct compared to Catalyst, which explains those results.
Overall, the RadeonSI Gallium3D driver is certainly coming into shape and becoming performant. In most of these Linux OpenGL game and benchmark tests the frame-rates were 50~75% the speed of the closed-source Catalyst driver. Mesa 10.0/10.1 and the Linux 3.13 kernel yield great results for this open-source AMD Linux graphics driver. The sore points for this driver are still though OpenCL support being enabled and only having OpenGL 3.1 compliance with it likely being many months before seeing GL4 compliance in the RadeonSI Gallium3D driver.
Coming up soon will be similar benchmarks to see how the mature Radeon R600 Gallium3D driver is comparing to Catalyst for Radeon HD 5000/6000 series graphics cards. To end, I'll repeat my comments from the beginning of this article... If you appreciate all of this frequent Linux graphics card and driver testing done exclusively at Phoronix, please consider subscribing to Phoronix Premium or making a PayPal tip. Premium subscribers are able to read entire articles (such as this one) on a single page and view the site without advertisements. If not a subscriber, at the very least please do not use AdBlock when reading Phoronix.com as it deprives much-needed revenue from the site that is expensive and very time consuming to operate; frequently I am still working 80+ hour weeks on Phoronix.